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 $21.83   7.551%   $23.4784   $23.48   $23.50   $23.50  
  Purchase #2 $119.37   13.239%   $135.1734   $135.17   $135.15   $135.20  
  Purchase #3 $201.37   5.742%   $212.9327   $212.93   $212.95   $212.90  
  Purchase #4 $223.68   3.410%   $231.3075   $231.31   $231.30   $231.30  
  Purchase #5 $204.73   11.797%   $228.882   $228.88   $228.90   $228.90  
  Purchase #6 $153.52   10.271%   $169.288   $169.29   $169.30   $169.30  
  Purchase #7 $63.34   4.546%   $66.2194   $66.22   $66.20   $66.20  
  7 purchase totals = $987.84       $1,067.2814   $1,067.28   $1,067.30   $1,067.30