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 $49.49   12.696%   $55.7733   $55.77   $55.75   $55.80  
  Purchase #2 $163.41   11.788%   $182.6728   $182.67   $182.65   $182.70  
  Purchase #3 $124.35   8.305%   $134.6773   $134.68   $134.70   $134.70  
  Purchase #4 $88.65   9.264%   $96.8625   $96.86   $96.85   $96.90  
  Purchase #5 $10.61   8.403%   $11.5016   $11.50   $11.50   $11.50  
  Purchase #6 $159.73   12.128%   $179.1021   $179.10   $179.10   $179.10  
  Purchase #7 $214.68   4.865%   $225.1242   $225.12   $225.10   $225.10  
  7 purchase totals = $810.92       $885.7138   $885.70   $885.65   $885.80