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	$250.45	11.201%	$278.5029	$278.50	$278.50	$278.50
Purchase #2	$47.97	5.400%	$50.5604	$50.56	$50.55	$50.60
Purchase #3	$145.75	3.654%	$151.0757	$151.08	$151.10	$151.10
Purchase #4	$146.83	3.391%	$151.809	$151.81	$151.80	$151.80
Purchase #5	$41.82	4.227%	$43.5877	$43.59	$43.60	$43.60
Purchase #6	$240.33	10.347%	$265.1969	$265.20	$265.20	$265.20
Purchase #7	$20.44	10.159%	$22.5165	$22.52	$22.50	$22.50
7 purchase totals =	$893.59		$963.2491	$963.26	$963.25	$963.30