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	$12.90	4.762%	$13.5143	$13.51	$13.50	$13.50
Purchase #2	$188.95	13.854%	$215.1271	$215.13	$215.15	$215.10
Purchase #3	$45.77	4.118%	$47.6548	$47.65	$47.65	$47.70
Purchase #4	$89.97	11.410%	$100.2356	$100.24	$100.25	$100.20
Purchase #5	$97.73	7.824%	$105.3764	$105.38	$105.40	$105.40
Purchase #6	$40.30	11.105%	$44.7753	$44.78	$44.80	$44.80
Purchase #7	$165.56	9.171%	$180.7435	$180.74	$180.75	$180.70
7 purchase totals =	$641.18		$707.4270	$707.43	$707.50	$707.40