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 $67.91   7.608%   $73.0766   $73.08   $73.10   $73.10  
  Purchase #2 $132.35   12.729%   $149.1968   $149.20   $149.20   $149.20  
  Purchase #3 $11.26   6.827%   $12.0287   $12.03   $12.05   $12.00  
  Purchase #4 $125.37   9.837%   $137.7026   $137.70   $137.70   $137.70  
  Purchase #5 $149.73   8.752%   $162.8344   $162.83   $162.85   $162.80  
  Purchase #6 $248.78   3.627%   $257.8033   $257.80   $257.80   $257.80  
  Purchase #7 $110.51   9.740%   $121.2737   $121.27   $121.25   $121.30  
  7 purchase totals = $845.91       $913.9161   $913.91   $913.95   $913.90