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 $186.64   8.771%   $203.0102   $203.01   $203.00   $203.00  
  Purchase #2 $192.43   3.381%   $198.9361   $198.94   $198.95   $198.90  
  Purchase #3 $48.52   5.397%   $51.1386   $51.14   $51.15   $51.10  
  Purchase #4 $54.79   7.398%   $58.8434   $58.84   $58.85   $58.80  
  Purchase #5 $131.84   4.208%   $137.3878   $137.39   $137.40   $137.40  
  Purchase #6 $64.84   5.733%   $68.5573   $68.56   $68.55   $68.60  
  Purchase #7 $45.85   11.578%   $51.1585   $51.16   $51.15   $51.20  
  7 purchase totals = $724.91       $769.0319   $769.04   $769.05   $769.00