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	$27.67	12.823%	$31.2181	$31.22	$31.20	$31.20
Purchase #2	$127.39	6.355%	$135.4856	$135.49	$135.50	$135.50
Purchase #3	$239.90	3.488%	$248.2677	$248.27	$248.25	$248.30
Purchase #4	$89.86	8.784%	$97.7533	$97.75	$97.75	$97.80
Purchase #5	$89.31	12.792%	$100.7345	$100.73	$100.75	$100.70
Purchase #6	$91.42	13.286%	$103.5661	$103.57	$103.55	$103.60
Purchase #7	$56.43	13.862%	$64.2523	$64.25	$64.25	$64.30
7 purchase totals =	$721.98		$781.2776	$781.28	$781.25	$781.40