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 $56.53   13.102%   $63.9366   $63.94   $63.95   $63.90  
  Purchase #2 $102.66   9.675%   $112.5924   $112.59   $112.60   $112.60  
  Purchase #3 $176.45   6.193%   $187.3775   $187.38   $187.40   $187.40  
  Purchase #4 $249.38   7.569%   $268.2556   $268.26   $268.25   $268.30  
  Purchase #5 $170.91   12.344%   $192.0071   $192.01   $192.00   $192.00  
  Purchase #6 $194.30   6.106%   $206.164   $206.16   $206.15   $206.20  
  Purchase #7 $48.94   7.352%   $52.5381   $52.54   $52.55   $52.50  
  7 purchase totals = $999.17       $1,082.8713   $1,082.88   $1,082.90   $1,082.90