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 $164.67   6.862%   $175.9697   $175.97   $175.95   $176.00  
  Purchase #2 $138.62   3.343%   $143.2541   $143.25   $143.25   $143.30  
  Purchase #3 $79.39   9.161%   $86.6629   $86.66   $86.65   $86.70  
  Purchase #4 $52.58   3.155%   $54.2389   $54.24   $54.25   $54.20  
  Purchase #5 $59.49   10.131%   $65.5169   $65.52   $65.50   $65.50  
  Purchase #6 $203.34   7.416%   $218.4197   $218.42   $218.40   $218.40  
  Purchase #7 $154.74   4.545%   $161.7729   $161.77   $161.75   $161.80  
  7 purchase totals = $852.83       $905.8351   $905.83   $905.75   $905.90