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 $184.58   12.111%   $206.9345   $206.93   $206.95   $206.90  
  Purchase #2 $58.61   13.389%   $66.4573   $66.46   $66.45   $66.50  
  Purchase #3 $107.25   12.362%   $120.5082   $120.51   $120.50   $120.50  
  Purchase #4 $191.84   7.549%   $206.322   $206.32   $206.30   $206.30  
  Purchase #5 $115.70   4.506%   $120.9134   $120.91   $120.90   $120.90  
  Purchase #6 $144.56   5.434%   $152.4154   $152.42   $152.40   $152.40  
  Purchase #7 $132.66   6.422%   $141.1794   $141.18   $141.20   $141.20  
  7 purchase totals = $935.20       $1,014.7302   $1,014.73   $1,014.70   $1,014.70