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 $105.94   10.274%   $116.8243   $116.82   $116.80   $116.80  
  Purchase #2 $30.72   5.396%   $32.3777   $32.38   $32.40   $32.40  
  Purchase #3 $229.90   5.184%   $241.818   $241.82   $241.80   $241.80  
  Purchase #4 $236.97   3.708%   $245.7568   $245.76   $245.75   $245.80  
  Purchase #5 $242.34   12.211%   $271.9321   $271.93   $271.95   $271.90  
  Purchase #6 $197.27   3.702%   $204.5729   $204.57   $204.55   $204.60  
  Purchase #7 $224.42   9.501%   $245.7421   $245.74   $245.75   $245.70  
  7 purchase totals = $1,267.56       $1,359.0239   $1,359.02   $1,359.00   $1,359.00