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 $18.34   8.680%   $19.9319   $19.93   $19.95   $19.90  
  Purchase #2 $9.60   5.690%   $10.1462   $10.15   $10.15   $10.10  
  Purchase #3 $88.81   13.475%   $100.7771   $100.78   $100.80   $100.80  
  Purchase #4 $43.85   12.221%   $49.2089   $49.21   $49.20   $49.20  
  Purchase #5 $33.92   5.750%   $35.8704   $35.87   $35.85   $35.90  
  Purchase #6 $119.61   7.463%   $128.5365   $128.54   $128.55   $128.50  
  Purchase #7 $161.32   8.511%   $175.0499   $175.05   $175.05   $175.00  
  7 purchase totals = $475.45       $519.5209   $519.53   $519.55   $519.40