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 $29.61   3.498%   $30.6458   $30.65   $30.65   $30.60  
  Purchase #2 $97.77   8.370%   $105.9533   $105.95   $105.95   $106.00  
  Purchase #3 $107.53   13.674%   $122.2337   $122.23   $122.25   $122.20  
  Purchase #4 $13.68   4.494%   $14.2948   $14.29   $14.30   $14.30  
  Purchase #5 $150.37   8.374%   $162.962   $162.96   $162.95   $163.00  
  Purchase #6 $103.79   9.181%   $113.319   $113.32   $113.30   $113.30  
  Purchase #7 $206.25   6.569%   $219.7986   $219.80   $219.80   $219.80  
  7 purchase totals = $709.00       $769.2072   $769.20   $769.20   $769.20