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 $67.58   3.337%   $69.8351   $69.84   $69.85   $69.80  
  Purchase #2 $246.52   6.172%   $261.7352   $261.74   $261.75   $261.70  
  Purchase #3 $151.87   7.659%   $163.5017   $163.50   $163.50   $163.50  
  Purchase #4 $202.38   13.118%   $228.9282   $228.93   $228.95   $228.90  
  Purchase #5 $99.52   11.568%   $111.0325   $111.03   $111.05   $111.00  
  Purchase #6 $246.63   4.599%   $257.9725   $257.97   $257.95   $258.00  
  Purchase #7 $232.70   4.733%   $243.7137   $243.71   $243.70   $243.70  
  7 purchase totals = $1,247.20       $1,336.7189   $1,336.72   $1,336.75   $1,336.60