Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $245.37   4.430%   $256.2399   $256.24   $256.25   $256.20  
  Purchase #2 $250.81   6.376%   $266.8016   $266.80   $266.80   $266.80  
  Purchase #3 $95.47   11.313%   $106.2705   $106.27   $106.25   $106.30  
  Purchase #4 $153.36   12.815%   $173.0131   $173.01   $173.00   $173.00  
  Purchase #5 $148.74   4.502%   $155.4363   $155.44   $155.45   $155.40  
  Purchase #6 $206.70   11.587%   $230.6503   $230.65   $230.65   $230.70  
  Purchase #7 $184.42   10.376%   $203.5554   $203.56   $203.55   $203.60  
  7 purchase totals = $1,284.87       $1,391.9671   $1,391.97   $1,391.95   $1,392.00