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 $60.79   13.728%   $69.1353   $69.14   $69.15   $69.10  
  Purchase #2 $176.90   13.417%   $200.6347   $200.63   $200.65   $200.60  
  Purchase #3 $15.53   5.814%   $16.4329   $16.43   $16.45   $16.40  
  Purchase #4 $240.60   10.823%   $266.6401   $266.64   $266.65   $266.60  
  Purchase #5 $167.61   3.169%   $172.9216   $172.92   $172.90   $172.90  
  Purchase #6 $9.78   12.189%   $10.9721   $10.97   $10.95   $11.00  
  Purchase #7 $221.33   11.432%   $246.6324   $246.63   $246.65   $246.60  
  7 purchase totals = $892.54       $983.3691   $983.36   $983.40   $983.20