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 $248.41   6.290%   $264.035   $264.04   $264.05   $264.00  
  Purchase #2 $18.50   9.271%   $20.2151   $20.22   $20.20   $20.20  
  Purchase #3 $118.42   10.864%   $131.2851   $131.29   $131.30   $131.30  
  Purchase #4 $225.95   8.488%   $245.1286   $245.13   $245.15   $245.10  
  Purchase #5 $114.69   12.377%   $128.8852   $128.89   $128.90   $128.90  
  Purchase #6 $53.60   5.660%   $56.6338   $56.63   $56.65   $56.60  
  Purchase #7 $195.44   6.353%   $207.8563   $207.86   $207.85   $207.90  
  7 purchase totals = $975.01       $1,054.0391   $1,054.06   $1,054.10   $1,054.00