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 $45.54   12.386%   $51.1806   $51.18   $51.20   $51.20  
  Purchase #2 $64.70   4.647%   $67.7066   $67.71   $67.70   $67.70  
  Purchase #3 $106.38   11.121%   $118.2105   $118.21   $118.20   $118.20  
  Purchase #4 $149.65   8.610%   $162.5349   $162.53   $162.55   $162.50  
  Purchase #5 $93.34   8.349%   $101.133   $101.13   $101.15   $101.10  
  Purchase #6 $139.51   5.434%   $147.091   $147.09   $147.10   $147.10  
  Purchase #7 $94.91   13.601%   $107.8187   $107.82   $107.80   $107.80  
  7 purchase totals = $694.03       $755.6753   $755.67   $755.70   $755.60