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 $204.80   10.706%   $226.7259   $226.73   $226.75   $226.70  
  Purchase #2 $11.46   13.299%   $12.9841   $12.98   $13.00   $13.00  
  Purchase #3 $205.88   4.393%   $214.9243   $214.92   $214.90   $214.90  
  Purchase #4 $83.88   10.547%   $92.7268   $92.73   $92.75   $92.70  
  Purchase #5 $45.67   4.614%   $47.7772   $47.78   $47.80   $47.80  
  Purchase #6 $201.73   3.610%   $209.0125   $209.01   $209.00   $209.00  
  Purchase #7 $151.78   5.367%   $159.926   $159.93   $159.95   $159.90  
  7 purchase totals = $905.20       $964.0768   $964.08   $964.15   $964.00