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 $79.78   3.617%   $82.6656   $82.67   $82.65   $82.70  
  Purchase #2 $152.31   8.718%   $165.5884   $165.59   $165.60   $165.60  
  Purchase #3 $73.76   11.566%   $82.2911   $82.29   $82.30   $82.30  
  Purchase #4 $72.60   5.317%   $76.4601   $76.46   $76.45   $76.50  
  Purchase #5 $215.71   8.282%   $233.5751   $233.58   $233.60   $233.60  
  Purchase #6 $167.77   5.627%   $177.2104   $177.21   $177.20   $177.20  
  Purchase #7 $16.50   4.284%   $17.2069   $17.21   $17.20   $17.20  
  7 purchase totals = $778.43       $834.9976   $835.01   $835.00   $835.10