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 $151.66   9.277%   $165.7295   $165.73   $165.75   $165.70  
  Purchase #2 $229.86   6.394%   $244.5572   $244.56   $244.55   $244.60  
  Purchase #3 $136.50   8.855%   $148.5871   $148.59   $148.60   $148.60  
  Purchase #4 $110.69   6.773%   $118.187   $118.19   $118.20   $118.20  
  Purchase #5 $45.29   4.647%   $47.3946   $47.39   $47.40   $47.40  
  Purchase #6 $41.47   13.217%   $46.9511   $46.95   $46.95   $47.00  
  Purchase #7 $60.79   6.274%   $64.604   $64.60   $64.60   $64.60  
  7 purchase totals = $776.26       $836.0105   $836.01   $836.05   $836.10