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 $186.73   10.605%   $206.5327   $206.53   $206.55   $206.50  
  Purchase #2 $114.78   8.388%   $124.4077   $124.41   $124.40   $124.40  
  Purchase #3 $226.85   13.356%   $257.1481   $257.15   $257.15   $257.10  
  Purchase #4 $29.43   5.247%   $30.9742   $30.97   $30.95   $31.00  
  Purchase #5 $29.72   10.872%   $32.9512   $32.95   $32.95   $33.00  
  Purchase #6 $207.74   12.262%   $233.2131   $233.21   $233.20   $233.20  
  Purchase #7 $172.60   5.146%   $181.482   $181.48   $181.50   $181.50  
  7 purchase totals = $967.85       $1,066.7090   $1,066.70   $1,066.70   $1,066.70