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 $29.95   11.567%   $33.4143   $33.41   $33.40   $33.40  
  Purchase #2 $202.57   11.528%   $225.9223   $225.92   $225.90   $225.90  
  Purchase #3 $137.55   9.773%   $150.9928   $150.99   $151.00   $151.00  
  Purchase #4 $74.42   6.468%   $79.2335   $79.23   $79.25   $79.20  
  Purchase #5 $41.94   12.453%   $47.1628   $47.16   $47.15   $47.20  
  Purchase #6 $79.70   12.756%   $89.8665   $89.87   $89.85   $89.90  
  Purchase #7 $95.41   4.288%   $99.5012   $99.50   $99.50   $99.50  
  7 purchase totals = $661.54       $726.0934   $726.08   $726.05   $726.10