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 $24.92   6.311%   $26.4927   $26.49   $26.50   $26.50  
  Purchase #2 $78.84   5.103%   $82.8632   $82.86   $82.85   $82.90  
  Purchase #3 $225.91   6.501%   $240.5964   $240.60   $240.60   $240.60  
  Purchase #4 $108.99   6.153%   $115.6962   $115.70   $115.70   $115.70  
  Purchase #5 $218.52   8.438%   $236.9587   $236.96   $236.95   $237.00  
  Purchase #6 $123.25   8.294%   $133.4724   $133.47   $133.45   $133.50  
  Purchase #7 $152.87   4.258%   $159.3792   $159.38   $159.40   $159.40  
  7 purchase totals = $933.30       $995.4588   $995.46   $995.45   $995.60