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 $213.52   13.813%   $243.0135   $243.01   $243.00   $243.00  
  Purchase #2 $228.63   3.346%   $236.28   $236.28   $236.30   $236.30  
  Purchase #3 $82.90   13.699%   $94.2565   $94.26   $94.25   $94.30  
  Purchase #4 $154.34   13.363%   $174.9645   $174.96   $174.95   $175.00  
  Purchase #5 $89.44   13.838%   $101.8167   $101.82   $101.80   $101.80  
  Purchase #6 $247.40   10.104%   $272.3973   $272.40   $272.40   $272.40  
  Purchase #7 $26.95   11.393%   $30.0204   $30.02   $30.00   $30.00  
  7 purchase totals = $1,043.18       $1,152.7489   $1,152.75   $1,152.70   $1,152.80