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 $72.53   4.143%   $75.5349   $75.53   $75.55   $75.50  
  Purchase #2 $188.81   6.851%   $201.7454   $201.75   $201.75   $201.70  
  Purchase #3 $61.60   3.415%   $63.7036   $63.70   $63.70   $63.70  
  Purchase #4 $42.42   13.593%   $48.1862   $48.19   $48.20   $48.20  
  Purchase #5 $228.50   11.792%   $255.4447   $255.44   $255.45   $255.40  
  Purchase #6 $66.87   9.293%   $73.0842   $73.08   $73.10   $73.10  
  Purchase #7 $242.74   6.709%   $259.0254   $259.03   $259.05   $259.00  
  7 purchase totals = $903.47       $976.7244   $976.72   $976.80   $976.60