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 $178.61   13.407%   $202.5562   $202.56   $202.55   $202.60  
  Purchase #2 $173.92   5.319%   $183.1708   $183.17   $183.15   $183.20  
  Purchase #3 $108.57   9.873%   $119.2891   $119.29   $119.30   $119.30  
  Purchase #4 $23.40   13.812%   $26.632   $26.63   $26.65   $26.60  
  Purchase #5 $101.56   5.371%   $107.0148   $107.01   $107.00   $107.00  
  Purchase #6 $59.84   10.213%   $65.9515   $65.95   $65.95   $66.00  
  Purchase #7 $134.99   11.780%   $150.8918   $150.89   $150.90   $150.90  
  7 purchase totals = $780.89       $855.5062   $855.50   $855.50   $855.60