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 $170.59   8.165%   $184.5187   $184.52   $184.50   $184.50  
  Purchase #2 $126.43   5.731%   $133.6757   $133.68   $133.70   $133.70  
  Purchase #3 $59.83   10.601%   $66.1726   $66.17   $66.15   $66.20  
  Purchase #4 $208.35   4.329%   $217.3695   $217.37   $217.35   $217.40  
  Purchase #5 $5.30   3.745%   $5.4985   $5.50   $5.50   $5.50  
  Purchase #6 $95.73   11.549%   $106.7859   $106.79   $106.80   $106.80  
  Purchase #7 $207.30   5.769%   $219.2591   $219.26   $219.25   $219.30  
  7 purchase totals = $873.53       $933.2800   $933.29   $933.25   $933.40