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 $168.61   9.511%   $184.6465   $184.65   $184.65   $184.60  
  Purchase #2 $104.31   9.827%   $114.5605   $114.56   $114.55   $114.60  
  Purchase #3 $69.92   13.712%   $79.5074   $79.51   $79.50   $79.50  
  Purchase #4 $227.81   12.276%   $255.776   $255.78   $255.80   $255.80  
  Purchase #5 $204.63   10.413%   $225.9381   $225.94   $225.95   $225.90  
  Purchase #6 $39.86   4.766%   $41.7597   $41.76   $41.75   $41.80  
  Purchase #7 $46.71   9.149%   $50.9835   $50.98   $51.00   $51.00  
  7 purchase totals = $861.85       $953.1717   $953.18   $953.20   $953.20