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 $200.87   13.110%   $227.2041   $227.20   $227.20   $227.20  
  Purchase #2 $57.56   7.693%   $61.9881   $61.99   $62.00   $62.00  
  Purchase #3 $92.98   11.827%   $103.9767   $103.98   $104.00   $104.00  
  Purchase #4 $209.55   8.369%   $227.0872   $227.09   $227.10   $227.10  
  Purchase #5 $119.53   9.779%   $131.2188   $131.22   $131.20   $131.20  
  Purchase #6 $242.65   5.492%   $255.9763   $255.98   $256.00   $256.00  
  Purchase #7 $84.66   8.606%   $91.9458   $91.95   $91.95   $91.90  
  7 purchase totals = $1,007.80       $1,099.3970   $1,099.41   $1,099.45   $1,099.40