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	$198.40	13.689%	$225.559	$225.56	$225.55	$225.60
Purchase #2	$210.63	4.621%	$220.3632	$220.36	$220.35	$220.40
Purchase #3	$40.45	4.251%	$42.1695	$42.17	$42.15	$42.20
Purchase #4	$93.30	10.749%	$103.3288	$103.33	$103.35	$103.30
Purchase #5	$92.98	7.735%	$100.172	$100.17	$100.15	$100.20
Purchase #6	$55.87	8.591%	$60.6698	$60.67	$60.65	$60.70
Purchase #7	$7.26	5.603%	$7.6668	$7.67	$7.65	$7.70
7 purchase totals =	$698.89		$759.9291	$759.93	$759.85	$760.10