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	$250.51	3.303%	$258.7843	$258.78	$258.80	$258.80
Purchase #2	$171.62	5.307%	$180.7279	$180.73	$180.75	$180.70
Purchase #3	$187.67	13.662%	$213.3095	$213.31	$213.30	$213.30
Purchase #4	$94.27	5.565%	$99.5161	$99.52	$99.50	$99.50
Purchase #5	$161.48	12.630%	$181.8749	$181.87	$181.85	$181.90
Purchase #6	$105.28	10.423%	$116.2533	$116.25	$116.25	$116.30
Purchase #7	$222.29	5.190%	$233.8269	$233.83	$233.85	$233.80
7 purchase totals =	$1,193.12		$1,284.2929	$1,284.29	$1,284.30	$1,284.30