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 $247.75   13.783%   $281.8974   $281.90   $281.90   $281.90  
  Purchase #2 $36.58   13.429%   $41.4923   $41.49   $41.50   $41.50  
  Purchase #3 $138.98   6.706%   $148.3   $148.30   $148.30   $148.30  
  Purchase #4 $73.45   3.786%   $76.2308   $76.23   $76.25   $76.20  
  Purchase #5 $168.44   13.539%   $191.2451   $191.25   $191.25   $191.20  
  Purchase #6 $116.74   12.445%   $131.2683   $131.27   $131.25   $131.30  
  Purchase #7 $98.93   4.300%   $103.184   $103.18   $103.20   $103.20  
  7 purchase totals = $880.87       $973.6179   $973.62   $973.65   $973.60