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	$55.41	8.635%	$60.1947	$60.19	$60.20	$60.20
Purchase #2	$115.75	10.482%	$127.8829	$127.88	$127.90	$127.90
Purchase #3	$82.89	9.123%	$90.4521	$90.45	$90.45	$90.50
Purchase #4	$63.73	3.274%	$65.8165	$65.82	$65.80	$65.80
Purchase #5	$135.68	6.409%	$144.3757	$144.38	$144.40	$144.40
Purchase #6	$195.71	11.590%	$218.3928	$218.39	$218.40	$218.40
Purchase #7	$179.65	5.795%	$190.0607	$190.06	$190.05	$190.10
7 purchase totals =	$828.82		$897.1754	$897.17	$897.20	$897.30