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 $6.78   4.153%   $7.0616   $7.06   $7.05   $7.10  
  Purchase #2 $103.98   12.129%   $116.5917   $116.59   $116.60   $116.60  
  Purchase #3 $60.47   6.737%   $64.5439   $64.54   $64.55   $64.50  
  Purchase #4 $42.44   8.830%   $46.1875   $46.19   $46.20   $46.20  
  Purchase #5 $212.25   13.508%   $240.9207   $240.92   $240.90   $240.90  
  Purchase #6 $249.63   12.854%   $281.7174   $281.72   $281.70   $281.70  
  Purchase #7 $51.59   10.781%   $57.1519   $57.15   $57.15   $57.20  
  7 purchase totals = $727.14       $814.1747   $814.17   $814.15   $814.20