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 $53.94   9.855%   $59.2558   $59.26   $59.25   $59.30  
  Purchase #2 $241.92   12.216%   $271.4729   $271.47   $271.45   $271.50  
  Purchase #3 $122.99   10.733%   $136.1905   $136.19   $136.20   $136.20  
  Purchase #4 $166.89   6.371%   $177.5226   $177.52   $177.50   $177.50  
  Purchase #5 $59.32   6.478%   $63.1627   $63.16   $63.15   $63.20  
  Purchase #6 $81.87   11.683%   $91.4349   $91.43   $91.45   $91.40  
  Purchase #7 $32.49   12.850%   $36.665   $36.67   $36.65   $36.70  
  7 purchase totals = $759.42       $835.7044   $835.70   $835.65   $835.80