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 $82.69   4.389%   $86.3193   $86.32   $86.30   $86.30  
  Purchase #2 $191.57   7.408%   $205.7615   $205.76   $205.75   $205.80  
  Purchase #3 $17.96   4.350%   $18.7413   $18.74   $18.75   $18.70  
  Purchase #4 $52.44   13.494%   $59.5163   $59.52   $59.50   $59.50  
  Purchase #5 $15.77   11.743%   $17.6219   $17.62   $17.60   $17.60  
  Purchase #6 $211.33   11.410%   $235.4428   $235.44   $235.45   $235.40  
  Purchase #7 $59.44   13.299%   $67.3449   $67.34   $67.35   $67.30  
  7 purchase totals = $631.20       $690.7480   $690.74   $690.70   $690.60