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	$30.41	11.498%	$33.9065	$33.91	$33.90	$33.90
Purchase #2	$71.86	12.768%	$81.0351	$81.04	$81.05	$81.00
Purchase #3	$220.91	10.171%	$243.3788	$243.38	$243.40	$243.40
Purchase #4	$8.91	13.284%	$10.0936	$10.09	$10.10	$10.10
Purchase #5	$125.81	11.545%	$140.3348	$140.33	$140.35	$140.30
Purchase #6	$133.25	6.802%	$142.3137	$142.31	$142.30	$142.30
Purchase #7	$13.43	13.235%	$15.2075	$15.21	$15.20	$15.20
7 purchase totals =	$604.58		$666.2700	$666.27	$666.30	$666.20