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	$105.47	3.819%	$109.4979	$109.50	$109.50	$109.50
Purchase #2	$57.33	7.320%	$61.5266	$61.53	$61.55	$61.50
Purchase #3	$46.94	13.125%	$53.1009	$53.10	$53.10	$53.10
Purchase #4	$30.63	4.493%	$32.0062	$32.01	$32.00	$32.00
Purchase #5	$138.85	6.809%	$148.3043	$148.30	$148.30	$148.30
Purchase #6	$85.76	4.854%	$89.9228	$89.92	$89.90	$89.90
Purchase #7	$146.93	9.825%	$161.3659	$161.37	$161.35	$161.40
7 purchase totals =	$611.91		$655.7246	$655.73	$655.70	$655.70