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 $72.55   3.754%   $75.2735   $75.27   $75.25   $75.30  
  Purchase #2 $163.36   6.127%   $173.3691   $173.37   $173.35   $173.40  
  Purchase #3 $179.26   9.195%   $195.743   $195.74   $195.75   $195.70  
  Purchase #4 $93.99   6.312%   $99.9226   $99.92   $99.90   $99.90  
  Purchase #5 $204.97   8.817%   $223.0422   $223.04   $223.05   $223.00  
  Purchase #6 $61.92   4.857%   $64.9275   $64.93   $64.95   $64.90  
  Purchase #7 $173.53   4.635%   $181.5731   $181.57   $181.55   $181.60  
  7 purchase totals = $949.58       $1,013.8510   $1,013.84   $1,013.80   $1,013.80