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 $244.96   8.265%   $265.2059   $265.21   $265.20   $265.20  
  Purchase #2 $226.51   5.317%   $238.5535   $238.55   $238.55   $238.60  
  Purchase #3 $17.47   10.812%   $19.3589   $19.36   $19.35   $19.40  
  Purchase #4 $116.48   5.810%   $123.2475   $123.25   $123.25   $123.20  
  Purchase #5 $195.97   9.443%   $214.4754   $214.48   $214.50   $214.50  
  Purchase #6 $130.95   13.468%   $148.5863   $148.59   $148.60   $148.60  
  Purchase #7 $213.81   9.358%   $233.8183   $233.82   $233.80   $233.80  
  7 purchase totals = $1,146.15       $1,243.2458   $1,243.26   $1,243.25   $1,243.30