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 $244.70   6.462%   $260.5125   $260.51   $260.50   $260.50  
  Purchase #2 $229.91   10.571%   $254.2138   $254.21   $254.20   $254.20  
  Purchase #3 $5.53   9.618%   $6.0619   $6.06   $6.05   $6.10  
  Purchase #4 $116.51   12.572%   $131.1576   $131.16   $131.15   $131.20  
  Purchase #5 $183.51   12.267%   $206.0212   $206.02   $206.00   $206.00  
  Purchase #6 $66.53   4.469%   $69.5032   $69.50   $69.50   $69.50  
  Purchase #7 $232.49   4.370%   $242.6498   $242.65   $242.65   $242.60  
  7 purchase totals = $1,079.18       $1,170.1200   $1,170.11   $1,170.05   $1,170.10