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	$205.93	13.825%	$234.3998	$234.40	$234.40	$234.40
Purchase #2	$201.40	10.788%	$223.127	$223.13	$223.15	$223.10
Purchase #3	$244.70	5.616%	$258.4424	$258.44	$258.45	$258.40
Purchase #4	$94.26	6.383%	$100.2766	$100.28	$100.30	$100.30
Purchase #5	$61.31	11.113%	$68.1234	$68.12	$68.10	$68.10
Purchase #6	$180.93	4.397%	$188.8855	$188.89	$188.90	$188.90
Purchase #7	$155.83	6.148%	$165.4104	$165.41	$165.40	$165.40
7 purchase totals =	$1,144.36		$1,238.6651	$1,238.67	$1,238.70	$1,238.60