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 $245.43   11.453%   $273.5391   $273.54   $273.55   $273.50  
  Purchase #2 $226.48   7.822%   $244.1953   $244.20   $244.20   $244.20  
  Purchase #3 $18.39   4.165%   $19.1559   $19.16   $19.15   $19.20  
  Purchase #4 $207.61   12.628%   $233.827   $233.83   $233.85   $233.80  
  Purchase #5 $56.56   8.438%   $61.3325   $61.33   $61.35   $61.30  
  Purchase #6 $138.66   9.526%   $151.8688   $151.87   $151.85   $151.90  
  Purchase #7 $139.63   6.130%   $148.1893   $148.19   $148.20   $148.20  
  7 purchase totals = $1,032.76       $1,132.1079   $1,132.12   $1,132.15   $1,132.10