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	$30.66	7.830%	$33.0607	$33.06	$33.05	$33.10
Purchase #2	$53.50	4.429%	$55.8695	$55.87	$55.85	$55.90
Purchase #3	$172.26	13.828%	$196.0801	$196.08	$196.10	$196.10
Purchase #4	$197.35	4.840%	$206.9017	$206.90	$206.90	$206.90
Purchase #5	$195.43	8.627%	$212.2897	$212.29	$212.30	$212.30
Purchase #6	$27.61	4.237%	$28.7798	$28.78	$28.80	$28.80
Purchase #7	$226.72	9.146%	$247.4558	$247.46	$247.45	$247.50
7 purchase totals =	$903.53		$980.4373	$980.44	$980.45	$980.60