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 $59.93   8.655%   $65.1169   $65.12   $65.10   $65.10  
  Purchase #2 $247.53   11.298%   $275.4959   $275.50   $275.50   $275.50  
  Purchase #3 $243.50   13.455%   $276.2629   $276.26   $276.25   $276.30  
  Purchase #4 $7.94   5.643%   $8.3881   $8.39   $8.40   $8.40  
  Purchase #5 $236.60   3.249%   $244.2871   $244.29   $244.30   $244.30  
  Purchase #6 $203.98   7.313%   $218.8971   $218.90   $218.90   $218.90  
  Purchase #7 $219.54   11.815%   $245.4787   $245.48   $245.50   $245.50  
  7 purchase totals = $1,219.02       $1,333.9267   $1,333.94   $1,333.95   $1,334.00