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 $112.44   3.119%   $115.947   $115.95   $115.95   $115.90  
  Purchase #2 $246.52   5.461%   $259.9825   $259.98   $260.00   $260.00  
  Purchase #3 $246.78   5.345%   $259.9704   $259.97   $259.95   $260.00  
  Purchase #4 $155.85   4.783%   $163.3043   $163.30   $163.30   $163.30  
  Purchase #5 $141.81   3.516%   $146.796   $146.80   $146.80   $146.80  
  Purchase #6 $122.56   5.648%   $129.4822   $129.48   $129.50   $129.50  
  Purchase #7 $184.92   3.385%   $191.1795   $191.18   $191.20   $191.20  
  7 purchase totals = $1,210.88       $1,266.6619   $1,266.66   $1,266.70   $1,266.70