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	$36.27	12.549%	$40.8215	$40.82	$40.80	$40.80
Purchase #2	$91.34	10.860%	$101.2595	$101.26	$101.25	$101.30
Purchase #3	$234.51	8.429%	$254.2768	$254.28	$254.30	$254.30
Purchase #4	$174.51	6.726%	$186.2475	$186.25	$186.25	$186.20
Purchase #5	$191.44	13.135%	$216.5856	$216.59	$216.60	$216.60
Purchase #6	$20.58	8.814%	$22.3939	$22.39	$22.40	$22.40
Purchase #7	$189.49	3.733%	$196.5637	$196.56	$196.55	$196.60
7 purchase totals =	$938.14		$1,018.1485	$1,018.15	$1,018.15	$1,018.20