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 $94.88   9.618%   $104.0056   $104.01   $104.00   $104.00  
  Purchase #2 $168.42   8.606%   $182.9142   $182.91   $182.90   $182.90  
  Purchase #3 $74.29   11.497%   $82.8311   $82.83   $82.85   $82.80  
  Purchase #4 $65.69   5.251%   $69.1394   $69.14   $69.15   $69.10  
  Purchase #5 $248.85   7.664%   $267.9219   $267.92   $267.90   $267.90  
  Purchase #6 $146.77   9.207%   $160.2831   $160.28   $160.30   $160.30  
  Purchase #7 $128.57   5.574%   $135.7365   $135.74   $135.75   $135.70  
  7 purchase totals = $927.47       $1,002.8318   $1,002.83   $1,002.85   $1,002.70