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	$73.41	9.396%	$80.3076	$80.31	$80.30	$80.30
Purchase #2	$43.73	3.161%	$45.1123	$45.11	$45.10	$45.10
Purchase #3	$100.63	10.636%	$111.333	$111.33	$111.35	$111.30
Purchase #4	$155.38	12.840%	$175.3308	$175.33	$175.35	$175.30
Purchase #5	$134.69	4.256%	$140.4224	$140.42	$140.40	$140.40
Purchase #6	$119.86	11.850%	$134.0634	$134.06	$134.05	$134.10
Purchase #7	$168.72	4.434%	$176.201	$176.20	$176.20	$176.20
7 purchase totals =	$796.42		$862.7705	$862.76	$862.75	$862.70