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	$89.82	9.128%	$98.0188	$98.02	$98.00	$98.00
Purchase #2	$112.50	12.251%	$126.2824	$126.28	$126.30	$126.30
Purchase #3	$11.73	6.162%	$12.4528	$12.45	$12.45	$12.50
Purchase #4	$38.43	5.690%	$40.6167	$40.62	$40.60	$40.60
Purchase #5	$37.53	13.180%	$42.4765	$42.48	$42.50	$42.50
Purchase #6	$110.60	4.366%	$115.4288	$115.43	$115.45	$115.40
Purchase #7	$50.33	6.820%	$53.7625	$53.76	$53.75	$53.80
7 purchase totals =	$450.94		$489.0385	$489.04	$489.05	$489.10