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	$86.72	3.340%	$89.6164	$89.62	$89.60	$89.60
Purchase #2	$206.88	7.580%	$222.5615	$222.56	$222.55	$222.60
Purchase #3	$137.40	13.655%	$156.162	$156.16	$156.15	$156.20
Purchase #4	$25.63	9.501%	$28.0651	$28.07	$28.05	$28.10
Purchase #5	$234.50	5.343%	$247.0293	$247.03	$247.05	$247.00
Purchase #6	$73.38	6.737%	$78.3236	$78.32	$78.30	$78.30
Purchase #7	$69.58	9.126%	$75.9299	$75.93	$75.95	$75.90
7 purchase totals =	$834.09		$897.6878	$897.69	$897.65	$897.70