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 $195.56   4.298%   $203.9652   $203.97   $203.95   $204.00  
  Purchase #2 $92.73   8.811%   $100.9004   $100.90   $100.90   $100.90  
  Purchase #3 $99.77   7.511%   $107.2637   $107.26   $107.25   $107.30  
  Purchase #4 $165.72   8.269%   $179.4234   $179.42   $179.40   $179.40  
  Purchase #5 $235.34   12.570%   $264.9222   $264.92   $264.90   $264.90  
  Purchase #6 $151.50   12.494%   $170.4284   $170.43   $170.45   $170.40  
  Purchase #7 $186.90   10.794%   $207.074   $207.07   $207.05   $207.10  
  7 purchase totals = $1,127.52       $1,233.9773   $1,233.97   $1,233.90   $1,234.00