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 $56.90   13.819%   $64.763   $64.76   $64.75   $64.80  
  Purchase #2 $200.80   8.439%   $217.7455   $217.75   $217.75   $217.70  
  Purchase #3 $7.98   8.330%   $8.6447   $8.64   $8.65   $8.60  
  Purchase #4 $232.60   13.181%   $263.259   $263.26   $263.25   $263.30  
  Purchase #5 $96.61   10.410%   $106.6671   $106.67   $106.65   $106.70  
  Purchase #6 $9.46   4.793%   $9.9134   $9.91   $9.90   $9.90  
  Purchase #7 $158.66   5.122%   $166.7866   $166.79   $166.80   $166.80  
  7 purchase totals = $763.01       $837.7793   $837.78   $837.75   $837.80