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 $237.42   6.461%   $252.7597   $252.76   $252.75   $252.80  
  Purchase #2 $55.56   11.706%   $62.0639   $62.06   $62.05   $62.10  
  Purchase #3 $215.61   5.378%   $227.2055   $227.21   $227.20   $227.20  
  Purchase #4 $58.56   7.433%   $62.9128   $62.91   $62.90   $62.90  
  Purchase #5 $222.94   8.637%   $242.1953   $242.20   $242.20   $242.20  
  Purchase #6 $155.93   11.470%   $173.8152   $173.82   $173.80   $173.80  
  Purchase #7 $124.90   6.230%   $132.6813   $132.68   $132.70   $132.70  
  7 purchase totals = $1,070.92       $1,153.6337   $1,153.64   $1,153.60   $1,153.70