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 $213.92   9.768%   $234.8157   $234.82   $234.80   $234.80  
  Purchase #2 $88.77   6.132%   $94.2134   $94.21   $94.20   $94.20  
  Purchase #3 $54.72   6.421%   $58.2336   $58.23   $58.25   $58.20  
  Purchase #4 $163.62   7.112%   $175.2567   $175.26   $175.25   $175.30  
  Purchase #5 $143.53   5.275%   $151.1012   $151.10   $151.10   $151.10  
  Purchase #6 $241.50   8.485%   $261.9913   $261.99   $262.00   $262.00  
  Purchase #7 $15.90   13.563%   $18.0565   $18.06   $18.05   $18.10  
  7 purchase totals = $921.96       $993.6684   $993.67   $993.65   $993.70