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 $243.54   8.536%   $264.3286   $264.33   $264.35   $264.30  
  Purchase #2 $185.70   7.402%   $199.4455   $199.45   $199.45   $199.40  
  Purchase #3 $154.64   10.317%   $170.5942   $170.59   $170.60   $170.60  
  Purchase #4 $178.44   6.395%   $189.8512   $189.85   $189.85   $189.90  
  Purchase #5 $76.85   12.212%   $86.2349   $86.23   $86.25   $86.20  
  Purchase #6 $250.62   13.340%   $284.0527   $284.05   $284.05   $284.10  
  Purchase #7 $183.56   7.628%   $197.562   $197.56   $197.55   $197.60  
  7 purchase totals = $1,273.35       $1,392.0691   $1,392.06   $1,392.10   $1,392.10