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	$250.48	9.194%	$273.5091	$273.51	$273.50	$273.50
Purchase #2	$142.53	4.109%	$148.3866	$148.39	$148.40	$148.40
Purchase #3	$10.44	6.350%	$11.1029	$11.10	$11.10	$11.10
Purchase #4	$75.92	8.850%	$82.6389	$82.64	$82.65	$82.60
Purchase #5	$32.72	6.237%	$34.7607	$34.76	$34.75	$34.80
Purchase #6	$87.39	12.733%	$98.5174	$98.52	$98.50	$98.50
Purchase #7	$37.28	11.215%	$41.461	$41.46	$41.45	$41.50
7 purchase totals =	$636.76		$690.3766	$690.38	$690.35	$690.40