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	$94.77	9.537%	$103.8082	$103.81	$103.80	$103.80
Purchase #2	$131.39	9.740%	$144.1874	$144.19	$144.20	$144.20
Purchase #3	$176.75	8.263%	$191.3549	$191.35	$191.35	$191.40
Purchase #4	$73.31	11.433%	$81.6915	$81.69	$81.70	$81.70
Purchase #5	$80.41	11.434%	$89.6041	$89.60	$89.60	$89.60
Purchase #6	$128.65	9.284%	$140.5939	$140.59	$140.60	$140.60
Purchase #7	$140.90	5.781%	$149.0454	$149.05	$149.05	$149.00
7 purchase totals =	$826.18		$900.2854	$900.28	$900.30	$900.30