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 $200.52   12.479%   $225.5429   $225.54   $225.55   $225.50  
  Purchase #2 $199.25   5.686%   $210.5794   $210.58   $210.60   $210.60  
  Purchase #3 $118.92   9.111%   $129.7548   $129.75   $129.75   $129.80  
  Purchase #4 $44.43   10.598%   $49.1387   $49.14   $49.15   $49.10  
  Purchase #5 $6.73   10.435%   $7.4323   $7.43   $7.45   $7.40  
  Purchase #6 $230.68   12.234%   $258.9014   $258.90   $258.90   $258.90  
  Purchase #7 $149.64   4.450%   $156.299   $156.30   $156.30   $156.30  
  7 purchase totals = $950.17       $1,037.6485   $1,037.64   $1,037.70   $1,037.60