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 $106.72   10.532%   $117.9598   $117.96   $117.95   $118.00  
  Purchase #2 $59.85   4.125%   $62.3188   $62.32   $62.30   $62.30  
  Purchase #3 $200.34   8.665%   $217.6995   $217.70   $217.70   $217.70  
  Purchase #4 $45.88   7.435%   $49.2912   $49.29   $49.30   $49.30  
  Purchase #5 $97.70   11.444%   $108.8808   $108.88   $108.90   $108.90  
  Purchase #6 $190.47   13.287%   $215.7777   $215.78   $215.80   $215.80  
  Purchase #7 $11.88   11.577%   $13.2553   $13.26   $13.25   $13.30  
  7 purchase totals = $712.84       $785.1831   $785.19   $785.20   $785.30