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 $234.48   4.234%   $244.4079   $244.41   $244.40   $244.40  
  Purchase #2 $128.86   5.355%   $135.7605   $135.76   $135.75   $135.80  
  Purchase #3 $45.88   9.645%   $50.3051   $50.31   $50.30   $50.30  
  Purchase #4 $191.32   12.408%   $215.059   $215.06   $215.05   $215.10  
  Purchase #5 $247.27   13.191%   $279.8874   $279.89   $279.90   $279.90  
  Purchase #6 $154.61   5.339%   $162.8646   $162.86   $162.85   $162.90  
  Purchase #7 $85.38   12.548%   $96.0935   $96.09   $96.10   $96.10  
  7 purchase totals = $1,087.80       $1,184.3780   $1,184.38   $1,184.35   $1,184.50