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 $98.29   8.282%   $106.4304   $106.43   $106.45   $106.40  
  Purchase #2 $28.68   12.413%   $32.24   $32.24   $32.25   $32.20  
  Purchase #3 $43.72   8.137%   $47.2775   $47.28   $47.30   $47.30  
  Purchase #4 $57.36   5.700%   $60.6295   $60.63   $60.65   $60.60  
  Purchase #5 $113.54   11.168%   $126.2201   $126.22   $126.20   $126.20  
  Purchase #6 $94.65   6.772%   $101.0597   $101.06   $101.05   $101.10  
  Purchase #7 $46.52   6.148%   $49.38   $49.38   $49.40   $49.40  
  7 purchase totals = $482.76       $523.2372   $523.24   $523.30   $523.20