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	$120.95	5.522%	$127.6289	$127.63	$127.65	$127.60
Purchase #2	$235.65	4.275%	$245.724	$245.72	$245.70	$245.70
Purchase #3	$45.33	5.270%	$47.7189	$47.72	$47.70	$47.70
Purchase #4	$138.73	10.336%	$153.0691	$153.07	$153.05	$153.10
Purchase #5	$16.90	4.386%	$17.6412	$17.64	$17.65	$17.60
Purchase #6	$145.84	4.498%	$152.3999	$152.40	$152.40	$152.40
Purchase #7	$57.41	3.167%	$59.2282	$59.23	$59.25	$59.20
7 purchase totals =	$760.81		$803.4102	$803.41	$803.40	$803.30