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 $68.82   8.203%   $74.4653   $74.47   $74.45   $74.50  
  Purchase #2 $227.27   12.182%   $254.956   $254.96   $254.95   $255.00  
  Purchase #3 $166.67   4.130%   $173.5535   $173.55   $173.55   $173.60  
  Purchase #4 $119.87   3.357%   $123.894   $123.89   $123.90   $123.90  
  Purchase #5 $81.84   7.440%   $87.9289   $87.93   $87.95   $87.90  
  Purchase #6 $98.78   6.677%   $105.3755   $105.38   $105.40   $105.40  
  Purchase #7 $155.42   6.281%   $165.1819   $165.18   $165.20   $165.20  
  7 purchase totals = $918.67       $985.3551   $985.36   $985.40   $985.50