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 $72.29   8.213%   $78.2272   $78.23   $78.25   $78.20  
  Purchase #2 $191.50   6.195%   $203.3634   $203.36   $203.35   $203.40  
  Purchase #3 $9.55   4.308%   $9.9614   $9.96   $9.95   $10.00  
  Purchase #4 $55.47   8.603%   $60.2421   $60.24   $60.25   $60.20  
  Purchase #5 $203.86   4.404%   $212.838   $212.84   $212.85   $212.80  
  Purchase #6 $238.85   10.172%   $263.1458   $263.15   $263.15   $263.10  
  Purchase #7 $171.53   13.591%   $194.8426   $194.84   $194.85   $194.80  
  7 purchase totals = $943.05       $1,022.6205   $1,022.62   $1,022.65   $1,022.50