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	$42.44	6.102%	$45.0297	$45.03	$45.05	$45.00
Purchase #2	$209.59	13.494%	$237.8721	$237.87	$237.85	$237.90
Purchase #3	$17.94	12.443%	$20.1723	$20.17	$20.15	$20.20
Purchase #4	$192.77	12.512%	$216.8894	$216.89	$216.90	$216.90
Purchase #5	$76.56	7.770%	$82.5087	$82.51	$82.50	$82.50
Purchase #6	$54.43	11.156%	$60.5022	$60.50	$60.50	$60.50
Purchase #7	$45.73	13.164%	$51.7499	$51.75	$51.75	$51.70
7 purchase totals =	$639.46		$714.7243	$714.72	$714.70	$714.70