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	$151.84	10.765%	$168.1856	$168.19	$168.20	$168.20
Purchase #2	$102.77	13.431%	$116.573	$116.57	$116.55	$116.60
Purchase #3	$235.89	8.873%	$256.8205	$256.82	$256.80	$256.80
Purchase #4	$165.69	13.189%	$187.5429	$187.54	$187.55	$187.50
Purchase #5	$58.96	9.119%	$64.3366	$64.34	$64.35	$64.30
Purchase #6	$172.57	13.644%	$196.1155	$196.12	$196.10	$196.10
Purchase #7	$250.38	6.762%	$267.3107	$267.31	$267.30	$267.30
7 purchase totals =	$1,138.10		$1,256.8848	$1,256.89	$1,256.85	$1,256.80