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	$69.40	11.187%	$77.1638	$77.16	$77.15	$77.20
Purchase #2	$130.97	3.405%	$135.4295	$135.43	$135.45	$135.40
Purchase #3	$38.89	9.260%	$42.4912	$42.49	$42.50	$42.50
Purchase #4	$165.67	13.155%	$187.4639	$187.46	$187.45	$187.50
Purchase #5	$54.66	5.446%	$57.6368	$57.64	$57.65	$57.60
Purchase #6	$92.67	7.688%	$99.7945	$99.79	$99.80	$99.80
Purchase #7	$7.63	9.131%	$8.3267	$8.33	$8.35	$8.30
7 purchase totals =	$559.89		$608.3064	$608.30	$608.35	$608.30