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	$205.40	8.821%	$223.5183	$223.52	$223.50	$223.50
Purchase #2	$181.79	8.479%	$197.204	$197.20	$197.20	$197.20
Purchase #3	$84.80	6.517%	$90.3264	$90.33	$90.35	$90.30
Purchase #4	$160.77	8.388%	$174.2554	$174.26	$174.25	$174.30
Purchase #5	$58.34	12.840%	$65.8309	$65.83	$65.85	$65.80
Purchase #6	$170.50	12.514%	$191.8364	$191.84	$191.85	$191.80
Purchase #7	$33.35	12.117%	$37.391	$37.39	$37.40	$37.40
7 purchase totals =	$894.95		$980.3624	$980.37	$980.40	$980.30