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 $231.96   6.584%   $247.2322   $247.23   $247.25   $247.20  
  Purchase #2 $180.60   10.399%   $199.3806   $199.38   $199.40   $199.40  
  Purchase #3 $215.25   13.390%   $244.072   $244.07   $244.05   $244.10  
  Purchase #4 $224.39   4.112%   $233.6169   $233.62   $233.60   $233.60  
  Purchase #5 $63.91   6.193%   $67.8679   $67.87   $67.85   $67.90  
  Purchase #6 $228.71   6.664%   $243.9512   $243.95   $243.95   $244.00  
  Purchase #7 $91.65   9.731%   $100.5685   $100.57   $100.55   $100.60  
  7 purchase totals = $1,236.47       $1,336.6893   $1,336.69   $1,336.65   $1,336.80