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 $49.95   10.679%   $55.2842   $55.28   $55.30   $55.30  
  Purchase #2 $202.46   11.594%   $225.9332   $225.93   $225.95   $225.90  
  Purchase #3 $6.99   10.763%   $7.7423   $7.74   $7.75   $7.70  
  Purchase #4 $243.65   7.553%   $262.0529   $262.05   $262.05   $262.10  
  Purchase #5 $45.69   4.664%   $47.821   $47.82   $47.80   $47.80  
  Purchase #6 $88.96   6.492%   $94.7353   $94.74   $94.75   $94.70  
  Purchase #7 $166.31   3.123%   $171.5039   $171.50   $171.50   $171.50  
  7 purchase totals = $804.01       $865.0728   $865.06   $865.10   $865.00