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 $243.43   12.861%   $274.7375   $274.74   $274.75   $274.70  
  Purchase #2 $195.26   10.385%   $215.5378   $215.54   $215.55   $215.50  
  Purchase #3 $190.37   3.350%   $196.7474   $196.75   $196.75   $196.70  
  Purchase #4 $67.98   10.559%   $75.158   $75.16   $75.15   $75.20  
  Purchase #5 $60.92   9.282%   $66.5746   $66.57   $66.55   $66.60  
  Purchase #6 $184.36   4.734%   $193.0876   $193.09   $193.10   $193.10  
  Purchase #7 $49.71   5.872%   $52.629   $52.63   $52.65   $52.60  
  7 purchase totals = $992.03       $1,074.4719   $1,074.48   $1,074.50   $1,074.40