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 $53.62   3.701%   $55.6045   $55.60   $55.60   $55.60  
  Purchase #2 $112.69   3.719%   $116.8809   $116.88   $116.90   $116.90  
  Purchase #3 $228.37   8.328%   $247.3887   $247.39   $247.40   $247.40  
  Purchase #4 $24.38   4.680%   $25.521   $25.52   $25.50   $25.50  
  Purchase #5 $60.25   13.356%   $68.297   $68.30   $68.30   $68.30  
  Purchase #6 $179.52   5.510%   $189.4116   $189.41   $189.40   $189.40  
  Purchase #7 $38.34   7.749%   $41.311   $41.31   $41.30   $41.30  
  7 purchase totals = $697.17       $744.4147   $744.41   $744.40   $744.40