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 $56.41   6.601%   $60.1336   $60.13   $60.15   $60.10  
  Purchase #2 $157.53   7.525%   $169.3841   $169.38   $169.40   $169.40  
  Purchase #3 $75.63   11.104%   $84.028   $84.03   $84.05   $84.00  
  Purchase #4 $93.60   8.609%   $101.658   $101.66   $101.65   $101.70  
  Purchase #5 $201.69   4.813%   $211.3973   $211.40   $211.40   $211.40  
  Purchase #6 $113.43   5.771%   $119.976   $119.98   $120.00   $120.00  
  Purchase #7 $214.43   8.106%   $231.8117   $231.81   $231.80   $231.80  
  7 purchase totals = $912.72       $978.3887   $978.39   $978.45   $978.40