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 $246.85   10.657%   $273.1568   $273.16   $273.15   $273.20  
  Purchase #2 $35.59   10.802%   $39.4344   $39.43   $39.45   $39.40  
  Purchase #3 $20.57   5.475%   $21.6962   $21.70   $21.70   $21.70  
  Purchase #4 $221.45   4.485%   $231.382   $231.38   $231.40   $231.40  
  Purchase #5 $203.70   4.227%   $212.3104   $212.31   $212.30   $212.30  
  Purchase #6 $215.73   8.645%   $234.3799   $234.38   $234.40   $234.40  
  Purchase #7 $215.44   10.421%   $237.891   $237.89   $237.90   $237.90  
  7 purchase totals = $1,159.33       $1,250.2507   $1,250.25   $1,250.30   $1,250.30