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 $93.93   13.178%   $106.3081   $106.31   $106.30   $106.30  
  Purchase #2 $211.46   12.526%   $237.9475   $237.95   $237.95   $237.90  
  Purchase #3 $25.47   5.485%   $26.867   $26.87   $26.85   $26.90  
  Purchase #4 $85.90   11.449%   $95.7347   $95.73   $95.75   $95.70  
  Purchase #5 $90.78   4.565%   $94.9241   $94.92   $94.90   $94.90  
  Purchase #6 $9.26   8.530%   $10.0499   $10.05   $10.05   $10.00  
  Purchase #7 $247.95   7.307%   $266.0677   $266.07   $266.05   $266.10  
  7 purchase totals = $764.75       $837.8990   $837.90   $837.85   $837.80