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 $168.77   11.457%   $188.106   $188.11   $188.10   $188.10  
  Purchase #2 $206.62   11.146%   $229.6499   $229.65   $229.65   $229.60  
  Purchase #3 $146.65   5.179%   $154.245   $154.25   $154.25   $154.20  
  Purchase #4 $85.33   7.784%   $91.9721   $91.97   $91.95   $92.00  
  Purchase #5 $107.56   5.569%   $113.55   $113.55   $113.55   $113.60  
  Purchase #6 $86.38   7.337%   $92.7177   $92.72   $92.70   $92.70  
  Purchase #7 $141.78   5.303%   $149.2986   $149.30   $149.30   $149.30  
  7 purchase totals = $943.09       $1,019.5393   $1,019.55   $1,019.50   $1,019.50