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 $229.86   7.211%   $246.4352   $246.44   $246.45   $246.40  
  Purchase #2 $104.91   12.126%   $117.6314   $117.63   $117.65   $117.60  
  Purchase #3 $202.50   10.524%   $223.8111   $223.81   $223.80   $223.80  
  Purchase #4 $126.81   7.441%   $136.2459   $136.25   $136.25   $136.20  
  Purchase #5 $114.99   3.521%   $119.0388   $119.04   $119.05   $119.00  
  Purchase #6 $232.58   6.604%   $247.9396   $247.94   $247.95   $247.90  
  Purchase #7 $241.85   13.219%   $273.8202   $273.82   $273.80   $273.80  
  7 purchase totals = $1,253.50       $1,364.9222   $1,364.93   $1,364.95   $1,364.70