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	$56.29	12.497%	$63.3246	$63.32	$63.30	$63.30
Purchase #2	$119.56	4.336%	$124.7441	$124.74	$124.75	$124.70
Purchase #3	$198.89	5.743%	$210.3123	$210.31	$210.30	$210.30
Purchase #4	$124.95	11.853%	$139.7603	$139.76	$139.75	$139.80
Purchase #5	$105.68	5.203%	$111.1785	$111.18	$111.20	$111.20
Purchase #6	$173.46	10.368%	$191.4443	$191.44	$191.45	$191.40
Purchase #7	$167.70	13.129%	$189.7173	$189.72	$189.70	$189.70
7 purchase totals =	$946.53		$1,030.4814	$1,030.47	$1,030.45	$1,030.40