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	$63.89	10.809%	$70.7959	$70.80	$70.80	$70.80
Purchase #2	$229.62	10.732%	$254.2628	$254.26	$254.25	$254.30
Purchase #3	$143.39	6.385%	$152.5455	$152.55	$152.55	$152.50
Purchase #4	$135.37	6.740%	$144.4939	$144.49	$144.50	$144.50
Purchase #5	$124.38	4.457%	$129.9236	$129.92	$129.90	$129.90
Purchase #6	$139.36	13.751%	$158.5234	$158.52	$158.50	$158.50
Purchase #7	$19.61	4.686%	$20.5289	$20.53	$20.55	$20.50
7 purchase totals =	$855.62		$931.0740	$931.07	$931.05	$931.00