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 $228.60   10.662%   $252.9733   $252.97   $252.95   $253.00  
  Purchase #2 $133.94   6.559%   $142.7251   $142.73   $142.75   $142.70  
  Purchase #3 $35.90   7.301%   $38.5211   $38.52   $38.50   $38.50  
  Purchase #4 $217.93   4.620%   $227.9984   $228.00   $228.00   $228.00  
  Purchase #5 $174.44   10.407%   $192.594   $192.59   $192.60   $192.60  
  Purchase #6 $176.99   3.354%   $182.9262   $182.93   $182.95   $182.90  
  Purchase #7 $163.89   7.366%   $175.9621   $175.96   $175.95   $176.00  
  7 purchase totals = $1,131.69       $1,213.7002   $1,213.70   $1,213.70   $1,213.70