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 $191.48   7.641%   $206.111   $206.11   $206.10   $206.10  
  Purchase #2 $245.27   8.723%   $266.6649   $266.66   $266.65   $266.70  
  Purchase #3 $101.82   8.414%   $110.3871   $110.39   $110.40   $110.40  
  Purchase #4 $224.55   3.576%   $232.5799   $232.58   $232.60   $232.60  
  Purchase #5 $179.28   7.279%   $192.3298   $192.33   $192.35   $192.30  
  Purchase #6 $34.54   4.156%   $35.9755   $35.98   $36.00   $36.00  
  Purchase #7 $34.98   13.807%   $39.8097   $39.81   $39.80   $39.80  
  7 purchase totals = $1,011.92       $1,083.8579   $1,083.86   $1,083.90   $1,083.90