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	$139.43	3.354%	$144.1065	$144.11	$144.10	$144.10
Purchase #2	$96.73	4.246%	$100.8372	$100.84	$100.85	$100.80
Purchase #3	$164.25	8.411%	$178.0651	$178.07	$178.05	$178.10
Purchase #4	$214.42	9.392%	$234.5583	$234.56	$234.55	$234.60
Purchase #5	$51.34	3.602%	$53.1893	$53.19	$53.20	$53.20
Purchase #6	$247.34	11.213%	$275.0742	$275.07	$275.05	$275.10
Purchase #7	$42.55	5.152%	$44.7422	$44.74	$44.75	$44.70
7 purchase totals =	$956.06		$1,030.5728	$1,030.58	$1,030.55	$1,030.60