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 $234.67   11.519%   $261.7016   $261.70   $261.70   $261.70  
  Purchase #2 $243.42   11.224%   $270.7415   $270.74   $270.75   $270.70  
  Purchase #3 $6.39   5.349%   $6.7318   $6.73   $6.75   $6.70  
  Purchase #4 $165.36   6.601%   $176.2754   $176.28   $176.30   $176.30  
  Purchase #5 $111.49   10.789%   $123.5187   $123.52   $123.50   $123.50  
  Purchase #6 $156.44   13.279%   $177.2137   $177.21   $177.20   $177.20  
  Purchase #7 $210.64   13.516%   $239.1101   $239.11   $239.10   $239.10  
  7 purchase totals = $1,128.41       $1,255.2928   $1,255.29   $1,255.30   $1,255.20