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 $231.94   6.579%   $247.1993   $247.20   $247.20   $247.20  
  Purchase #2 $154.85   13.107%   $175.1462   $175.15   $175.15   $175.10  
  Purchase #3 $173.33   11.598%   $193.4328   $193.43   $193.45   $193.40  
  Purchase #4 $20.44   11.502%   $22.791   $22.79   $22.80   $22.80  
  Purchase #5 $135.76   13.715%   $154.3795   $154.38   $154.40   $154.40  
  Purchase #6 $157.32   7.684%   $169.4085   $169.41   $169.40   $169.40  
  Purchase #7 $50.37   7.732%   $54.2646   $54.26   $54.25   $54.30  
  7 purchase totals = $924.01       $1,016.6219   $1,016.62   $1,016.65   $1,016.60