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	$169.84	12.743%	$191.4827	$191.48	$191.50	$191.50
Purchase #2	$18.80	9.135%	$20.5174	$20.52	$20.50	$20.50
Purchase #3	$51.75	8.874%	$56.3423	$56.34	$56.35	$56.30
Purchase #4	$39.55	7.173%	$42.3869	$42.39	$42.40	$42.40
Purchase #5	$245.43	6.821%	$262.1708	$262.17	$262.15	$262.20
Purchase #6	$126.75	9.681%	$139.0207	$139.02	$139.00	$139.00
Purchase #7	$154.30	7.253%	$165.4914	$165.49	$165.50	$165.50
7 purchase totals =	$806.42		$877.4122	$877.41	$877.40	$877.40