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 $48.64   8.872%   $52.9553   $52.96   $52.95   $53.00  
  Purchase #2 $55.86   13.115%   $63.186   $63.19   $63.20   $63.20  
  Purchase #3 $70.69   7.371%   $75.9006   $75.90   $75.90   $75.90  
  Purchase #4 $76.95   11.353%   $85.6861   $85.69   $85.70   $85.70  
  Purchase #5 $168.65   4.162%   $175.6692   $175.67   $175.65   $175.70  
  Purchase #6 $154.80   7.248%   $166.0199   $166.02   $166.00   $166.00  
  Purchase #7 $87.76   12.636%   $98.8494   $98.85   $98.85   $98.80  
  7 purchase totals = $663.35       $718.2665   $718.28   $718.25   $718.30