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	$69.90	10.489%	$77.2318	$77.23	$77.25	$77.20
Purchase #2	$72.32	6.354%	$76.9152	$76.92	$76.90	$76.90
Purchase #3	$151.73	13.319%	$171.9389	$171.94	$171.95	$171.90
Purchase #4	$223.93	10.521%	$247.4897	$247.49	$247.50	$247.50
Purchase #5	$14.40	3.125%	$14.85	$14.85	$14.85	$14.90
Purchase #6	$55.40	11.260%	$61.638	$61.64	$61.65	$61.60
Purchase #7	$59.91	10.539%	$66.2239	$66.22	$66.20	$66.20
7 purchase totals =	$647.59		$716.2875	$716.29	$716.30	$716.20