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 $63.56   13.197%   $71.948   $71.95   $71.95   $71.90  
  Purchase #2 $94.73   4.483%   $98.9767   $98.98   $99.00   $99.00  
  Purchase #3 $204.37   11.425%   $227.7193   $227.72   $227.70   $227.70  
  Purchase #4 $208.76   6.105%   $221.5048   $221.50   $221.50   $221.50  
  Purchase #5 $7.97   5.528%   $8.4106   $8.41   $8.40   $8.40  
  Purchase #6 $148.95   12.728%   $167.9084   $167.91   $167.90   $167.90  
  Purchase #7 $45.35   3.263%   $46.8298   $46.83   $46.85   $46.80  
  7 purchase totals = $773.69       $843.2976   $843.30   $843.30   $843.20