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 $188.99   8.396%   $204.8576   $204.86   $204.85   $204.90  
  Purchase #2 $47.26   12.804%   $53.3112   $53.31   $53.30   $53.30  
  Purchase #3 $235.63   5.450%   $248.4718   $248.47   $248.45   $248.50  
  Purchase #4 $204.85   12.870%   $231.2142   $231.21   $231.20   $231.20  
  Purchase #5 $58.74   9.794%   $64.493   $64.49   $64.50   $64.50  
  Purchase #6 $88.56   4.519%   $92.562   $92.56   $92.55   $92.60  
  Purchase #7 $112.30   4.677%   $117.5523   $117.55   $117.55   $117.60  
  7 purchase totals = $936.33       $1,012.4621   $1,012.45   $1,012.40   $1,012.60