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	$82.52	9.580%	$90.4254	$90.43	$90.45	$90.40
Purchase #2	$56.76	13.740%	$64.5588	$64.56	$64.55	$64.60
Purchase #3	$48.44	9.367%	$52.9774	$52.98	$53.00	$53.00
Purchase #4	$135.96	10.390%	$150.0862	$150.09	$150.10	$150.10
Purchase #5	$171.41	4.460%	$179.0549	$179.05	$179.05	$179.10
Purchase #6	$177.88	8.565%	$193.1154	$193.12	$193.10	$193.10
Purchase #7	$57.76	3.763%	$59.9335	$59.93	$59.95	$59.90
7 purchase totals =	$730.73		$790.1516	$790.16	$790.20	$790.20