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 $224.98   10.703%   $249.0596   $249.06   $249.05   $249.10  
  Purchase #2 $230.64   6.804%   $246.3327   $246.33   $246.35   $246.30  
  Purchase #3 $24.46   13.133%   $27.6723   $27.67   $27.65   $27.70  
  Purchase #4 $108.85   3.165%   $112.2951   $112.30   $112.30   $112.30  
  Purchase #5 $122.66   8.860%   $133.5277   $133.53   $133.55   $133.50  
  Purchase #6 $107.91   13.865%   $122.8717   $122.87   $122.85   $122.90  
  Purchase #7 $238.45   5.840%   $252.3755   $252.38   $252.40   $252.40  
  7 purchase totals = $1,057.95       $1,144.1346   $1,144.14   $1,144.15   $1,144.20