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	$90.88	10.343%	$100.2797	$100.28	$100.30	$100.30
Purchase #2	$210.92	11.699%	$235.5955	$235.60	$235.60	$235.60
Purchase #3	$130.63	7.461%	$140.3763	$140.38	$140.40	$140.40
Purchase #4	$185.27	7.386%	$198.954	$198.95	$198.95	$199.00
Purchase #5	$241.34	3.799%	$250.5085	$250.51	$250.50	$250.50
Purchase #6	$127.97	10.861%	$141.8688	$141.87	$141.85	$141.90
Purchase #7	$15.95	8.520%	$17.3089	$17.31	$17.30	$17.30
7 purchase totals =	$1,002.96		$1,084.8917	$1,084.90	$1,084.90	$1,085.00