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	$38.43	9.550%	$42.1001	$42.10	$42.10	$42.10
Purchase #2	$43.37	4.758%	$45.4335	$45.43	$45.45	$45.40
Purchase #3	$246.31	3.682%	$255.3791	$255.38	$255.40	$255.40
Purchase #4	$129.64	12.700%	$146.1043	$146.10	$146.10	$146.10
Purchase #5	$216.33	7.639%	$232.8554	$232.86	$232.85	$232.90
Purchase #6	$157.60	13.601%	$179.0352	$179.04	$179.05	$179.00
Purchase #7	$148.93	7.324%	$159.8376	$159.84	$159.85	$159.80
7 purchase totals =	$980.61		$1,060.7452	$1,060.75	$1,060.80	$1,060.70