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 $72.69   12.762%   $81.9667   $81.97   $81.95   $82.00  
  Purchase #2 $87.78   7.586%   $94.439   $94.44   $94.45   $94.40  
  Purchase #3 $52.55   7.486%   $56.4839   $56.48   $56.50   $56.50  
  Purchase #4 $216.35   12.249%   $242.8507   $242.85   $242.85   $242.90  
  Purchase #5 $116.91   7.495%   $125.6724   $125.67   $125.65   $125.70  
  Purchase #6 $159.59   4.566%   $166.8769   $166.88   $166.90   $166.90  
  Purchase #7 $86.75   4.187%   $90.3822   $90.38   $90.40   $90.40  
  7 purchase totals = $792.62       $858.6718   $858.67   $858.70   $858.80