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 $84.38   10.168%   $92.9598   $92.96   $92.95   $93.00  
  Purchase #2 $147.87   13.657%   $168.0646   $168.06   $168.05   $168.10  
  Purchase #3 $211.39   5.573%   $223.1708   $223.17   $223.15   $223.20  
  Purchase #4 $205.89   9.117%   $224.661   $224.66   $224.65   $224.70  
  Purchase #5 $47.84   7.471%   $51.4141   $51.41   $51.40   $51.40  
  Purchase #6 $57.30   5.872%   $60.6647   $60.66   $60.65   $60.70  
  Purchase #7 $85.63   5.516%   $90.3534   $90.35   $90.35   $90.40  
  7 purchase totals = $840.30       $911.2884   $911.27   $911.20   $911.50