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 $213.39   8.274%   $231.0459   $231.05   $231.05   $231.00  
  Purchase #2 $237.56   10.499%   $262.5014   $262.50   $262.50   $262.50  
  Purchase #3 $68.29   13.650%   $77.6116   $77.61   $77.60   $77.60  
  Purchase #4 $229.86   10.350%   $253.6505   $253.65   $253.65   $253.70  
  Purchase #5 $31.83   11.555%   $35.508   $35.51   $35.50   $35.50  
  Purchase #6 $14.90   8.729%   $16.2006   $16.20   $16.20   $16.20  
  Purchase #7 $5.77   9.569%   $6.3221   $6.32   $6.30   $6.30  
  7 purchase totals = $801.60       $882.8401   $882.84   $882.80   $882.80