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	$173.73	3.144%	$179.1921	$179.19	$179.20	$179.20
Purchase #2	$156.93	5.229%	$165.1359	$165.14	$165.15	$165.10
Purchase #3	$226.59	12.690%	$255.3443	$255.34	$255.35	$255.30
Purchase #4	$34.43	8.539%	$37.37	$37.37	$37.35	$37.40
Purchase #5	$145.73	3.263%	$150.4852	$150.49	$150.50	$150.50
Purchase #6	$75.71	12.692%	$85.3191	$85.32	$85.30	$85.30
Purchase #7	$134.91	10.307%	$148.8152	$148.82	$148.80	$148.80
7 purchase totals =	$948.03		$1,021.6618	$1,021.67	$1,021.65	$1,021.60