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 $57.77   10.734%   $63.971   $63.97   $63.95   $64.00  
  Purchase #2 $21.37   11.732%   $23.8771   $23.88   $23.90   $23.90  
  Purchase #3 $116.43   10.485%   $128.6377   $128.64   $128.65   $128.60  
  Purchase #4 $69.57   3.365%   $71.911   $71.91   $71.90   $71.90  
  Purchase #5 $204.86   6.677%   $218.5385   $218.54   $218.55   $218.50  
  Purchase #6 $8.54   12.590%   $9.6152   $9.62   $9.60   $9.60  
  Purchase #7 $9.99   8.575%   $10.8466   $10.85   $10.85   $10.80  
  7 purchase totals = $488.53       $527.3971   $527.41   $527.40   $527.30