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	$214.91	12.726%	$242.2594	$242.26	$242.25	$242.30
Purchase #2	$174.77	7.728%	$188.2762	$188.28	$188.30	$188.30
Purchase #3	$220.42	13.526%	$250.234	$250.23	$250.25	$250.20
Purchase #4	$32.82	12.506%	$36.9245	$36.92	$36.90	$36.90
Purchase #5	$123.61	13.141%	$139.8536	$139.85	$139.85	$139.90
Purchase #6	$90.75	7.733%	$97.7677	$97.77	$97.75	$97.80
Purchase #7	$44.26	9.673%	$48.5413	$48.54	$48.55	$48.50
7 purchase totals =	$901.54		$1,003.8567	$1,003.85	$1,003.85	$1,003.90