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 $41.95   12.442%   $47.1694   $47.17   $47.15   $47.20  
  Purchase #2 $219.55   3.824%   $227.9456   $227.95   $227.95   $227.90  
  Purchase #3 $96.56   5.156%   $101.5386   $101.54   $101.55   $101.50  
  Purchase #4 $72.62   3.343%   $75.0477   $75.05   $75.05   $75.00  
  Purchase #5 $204.49   12.163%   $229.3621   $229.36   $229.35   $229.40  
  Purchase #6 $207.31   12.342%   $232.8962   $232.90   $232.90   $232.90  
  Purchase #7 $113.96   9.105%   $124.3361   $124.34   $124.35   $124.30  
  7 purchase totals = $956.44       $1,038.2957   $1,038.31   $1,038.30   $1,038.20