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 $241.67   13.785%   $274.9842   $274.98   $275.00   $275.00  
  Purchase #2 $151.93   12.751%   $171.3026   $171.30   $171.30   $171.30  
  Purchase #3 $83.73   8.236%   $90.626   $90.63   $90.65   $90.60  
  Purchase #4 $246.87   12.409%   $277.5041   $277.50   $277.50   $277.50  
  Purchase #5 $133.70   9.204%   $146.0057   $146.01   $146.00   $146.00  
  Purchase #6 $239.37   10.522%   $264.5565   $264.56   $264.55   $264.60  
  Purchase #7 $118.32   6.834%   $126.406   $126.41   $126.40   $126.40  
  7 purchase totals = $1,215.59       $1,351.3851   $1,351.39   $1,351.40   $1,351.40