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 $100.48   4.785%   $105.288   $105.29   $105.30   $105.30  
  Purchase #2 $94.55   4.164%   $98.4871   $98.49   $98.50   $98.50  
  Purchase #3 $119.28   12.464%   $134.1471   $134.15   $134.15   $134.10  
  Purchase #4 $67.95   10.146%   $74.8442   $74.84   $74.85   $74.80  
  Purchase #5 $53.55   7.167%   $57.3879   $57.39   $57.40   $57.40  
  Purchase #6 $182.92   3.135%   $188.6545   $188.65   $188.65   $188.70  
  Purchase #7 $18.49   13.169%   $20.9249   $20.92   $20.90   $20.90  
  7 purchase totals = $637.22       $679.7337   $679.73   $679.75   $679.70