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 $229.78   8.350%   $248.9666   $248.97   $248.95   $249.00  
  Purchase #2 $154.98   9.272%   $169.3497   $169.35   $169.35   $169.30  
  Purchase #3 $72.56   13.226%   $82.1568   $82.16   $82.15   $82.20  
  Purchase #4 $222.71   10.533%   $246.168   $246.17   $246.15   $246.20  
  Purchase #5 $221.32   8.866%   $240.9422   $240.94   $240.95   $240.90  
  Purchase #6 $116.96   6.869%   $124.994   $124.99   $125.00   $125.00  
  Purchase #7 $188.75   13.452%   $214.1407   $214.14   $214.15   $214.10  
  7 purchase totals = $1,207.06       $1,326.7180   $1,326.72   $1,326.70   $1,326.70