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 $227.66   7.437%   $244.5911   $244.59   $244.60   $244.60  
  Purchase #2 $118.53   5.129%   $124.6094   $124.61   $124.60   $124.60  
  Purchase #3 $178.86   11.217%   $198.9227   $198.92   $198.90   $198.90  
  Purchase #4 $229.74   9.451%   $251.4527   $251.45   $251.45   $251.50  
  Purchase #5 $227.51   10.300%   $250.9435   $250.94   $250.95   $250.90  
  Purchase #6 $24.74   4.860%   $25.9424   $25.94   $25.95   $25.90  
  Purchase #7 $149.48   11.859%   $167.2068   $167.21   $167.20   $167.20  
  7 purchase totals = $1,156.52       $1,263.6686   $1,263.66   $1,263.65   $1,263.60