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 $201.32   11.774%   $225.0234   $225.02   $225.00   $225.00  
  Purchase #2 $137.39   8.287%   $148.7755   $148.78   $148.80   $148.80  
  Purchase #3 $227.79   4.216%   $237.3936   $237.39   $237.40   $237.40  
  Purchase #4 $19.26   6.768%   $20.5635   $20.56   $20.55   $20.60  
  Purchase #5 $135.86   11.134%   $150.9867   $150.99   $151.00   $151.00  
  Purchase #6 $98.85   13.168%   $111.8666   $111.87   $111.85   $111.90  
  Purchase #7 $119.25   11.274%   $132.6942   $132.69   $132.70   $132.70  
  7 purchase totals = $939.72       $1,027.3035   $1,027.30   $1,027.30   $1,027.40