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 $246.67   7.611%   $265.4441   $265.44   $265.45   $265.40  
  Purchase #2 $13.68   10.513%   $15.1182   $15.12   $15.10   $15.10  
  Purchase #3 $193.68   8.715%   $210.5592   $210.56   $210.55   $210.60  
  Purchase #4 $115.98   12.551%   $130.5366   $130.54   $130.55   $130.50  
  Purchase #5 $139.89   12.686%   $157.6364   $157.64   $157.65   $157.60  
  Purchase #6 $179.55   8.772%   $195.3001   $195.30   $195.30   $195.30  
  Purchase #7 $36.55   13.713%   $41.5621   $41.56   $41.55   $41.60  
  7 purchase totals = $926.00       $1,016.1567   $1,016.16   $1,016.15   $1,016.10