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 $61.67   7.517%   $66.3057   $66.31   $66.30   $66.30  
  Purchase #2 $219.74   7.146%   $235.4426   $235.44   $235.45   $235.40  
  Purchase #3 $182.85   4.350%   $190.804   $190.80   $190.80   $190.80  
  Purchase #4 $85.94   3.275%   $88.7545   $88.75   $88.75   $88.80  
  Purchase #5 $147.49   8.807%   $160.4794   $160.48   $160.50   $160.50  
  Purchase #6 $245.43   7.733%   $264.4091   $264.41   $264.40   $264.40  
  Purchase #7 $95.54   7.834%   $103.0246   $103.02   $103.00   $103.00  
  7 purchase totals = $1,038.66       $1,109.2199   $1,109.21   $1,109.20   $1,109.20