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 $58.94   4.819%   $61.7803   $61.78   $61.80   $61.80  
  Purchase #2 $98.65   12.175%   $110.6606   $110.66   $110.65   $110.70  
  Purchase #3 $40.65   4.241%   $42.374   $42.37   $42.35   $42.40  
  Purchase #4 $184.67   9.635%   $202.463   $202.46   $202.45   $202.50  
  Purchase #5 $91.55   12.291%   $102.8024   $102.80   $102.80   $102.80  
  Purchase #6 $152.97   6.183%   $162.4281   $162.43   $162.45   $162.40  
  Purchase #7 $129.90   12.873%   $146.622   $146.62   $146.60   $146.60  
  7 purchase totals = $757.33       $829.1304   $829.12   $829.10   $829.20