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 $62.33   8.579%   $67.6773   $67.68   $67.70   $67.70  
  Purchase #2 $95.88   12.861%   $108.2111   $108.21   $108.20   $108.20  
  Purchase #3 $63.77   4.298%   $66.5108   $66.51   $66.50   $66.50  
  Purchase #4 $74.50   11.572%   $83.1211   $83.12   $83.10   $83.10  
  Purchase #5 $227.88   6.226%   $242.0678   $242.07   $242.05   $242.10  
  Purchase #6 $119.56   5.731%   $126.412   $126.41   $126.40   $126.40  
  Purchase #7 $70.77   11.778%   $79.1053   $79.11   $79.10   $79.10  
  7 purchase totals = $714.69       $773.1054   $773.11   $773.05   $773.10