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	$141.96	3.211%	$146.5183	$146.52	$146.50	$146.50
Purchase #2	$109.92	5.789%	$116.2833	$116.28	$116.30	$116.30
Purchase #3	$235.44	12.335%	$264.4815	$264.48	$264.50	$264.50
Purchase #4	$168.68	5.690%	$178.2779	$178.28	$178.30	$178.30
Purchase #5	$218.57	6.683%	$233.177	$233.18	$233.20	$233.20
Purchase #6	$57.39	7.460%	$61.6713	$61.67	$61.65	$61.70
Purchase #7	$223.70	11.236%	$248.8349	$248.83	$248.85	$248.80
7 purchase totals =	$1,155.66		$1,249.2442	$1,249.24	$1,249.30	$1,249.30