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	$84.44	7.490%	$90.7646	$90.76	$90.75	$90.80
Purchase #2	$33.73	4.670%	$35.3052	$35.31	$35.30	$35.30
Purchase #3	$173.49	6.685%	$185.0878	$185.09	$185.10	$185.10
Purchase #4	$240.59	4.723%	$251.9531	$251.95	$251.95	$252.00
Purchase #5	$26.86	13.567%	$30.5041	$30.50	$30.50	$30.50
Purchase #6	$202.43	10.518%	$223.7216	$223.72	$223.70	$223.70
Purchase #7	$76.28	3.471%	$78.9277	$78.93	$78.95	$78.90
7 purchase totals =	$837.82		$896.2641	$896.26	$896.25	$896.30