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 $217.61   13.340%   $246.6392   $246.64   $246.65   $246.60  
  Purchase #2 $47.77   13.665%   $54.2978   $54.30   $54.30   $54.30  
  Purchase #3 $63.70   11.485%   $71.0159   $71.02   $71.00   $71.00  
  Purchase #4 $101.68   6.128%   $107.911   $107.91   $107.90   $107.90  
  Purchase #5 $76.79   7.103%   $82.2444   $82.24   $82.25   $82.20  
  Purchase #6 $5.82   13.679%   $6.6161   $6.62   $6.60   $6.60  
  Purchase #7 $159.71   3.759%   $165.7135   $165.71   $165.70   $165.70  
  7 purchase totals = $673.08       $734.4379   $734.44   $734.40   $734.30