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	$64.69	10.108%	$71.2289	$71.23	$71.25	$71.20
Purchase #2	$131.66	8.547%	$142.913	$142.91	$142.90	$142.90
Purchase #3	$139.73	6.363%	$148.621	$148.62	$148.60	$148.60
Purchase #4	$195.75	8.116%	$211.6371	$211.64	$211.65	$211.60
Purchase #5	$100.91	7.852%	$108.8335	$108.83	$108.85	$108.80
Purchase #6	$241.67	12.807%	$272.6207	$272.62	$272.60	$272.60
Purchase #7	$128.61	12.406%	$144.5654	$144.57	$144.55	$144.60
7 purchase totals =	$1,003.02		$1,100.4196	$1,100.42	$1,100.40	$1,100.30