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 $68.98   6.690%   $73.5948   $73.59   $73.60   $73.60  
  Purchase #2 $130.53   3.293%   $134.8284   $134.83   $134.85   $134.80  
  Purchase #3 $32.71   4.572%   $34.2055   $34.21   $34.20   $34.20  
  Purchase #4 $204.86   9.113%   $223.5289   $223.53   $223.55   $223.50  
  Purchase #5 $133.86   5.119%   $140.7123   $140.71   $140.70   $140.70  
  Purchase #6 $219.90   6.358%   $233.8812   $233.88   $233.90   $233.90  
  Purchase #7 $196.96   4.791%   $206.3964   $206.40   $206.40   $206.40  
  7 purchase totals = $987.80       $1,047.1475   $1,047.15   $1,047.20   $1,047.10