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	$250.85	9.344%	$274.2894	$274.29	$274.30	$274.30
Purchase #2	$64.96	11.845%	$72.6545	$72.65	$72.65	$72.70
Purchase #3	$23.57	7.579%	$25.3564	$25.36	$25.35	$25.40
Purchase #4	$61.74	4.448%	$64.4862	$64.49	$64.50	$64.50
Purchase #5	$81.56	10.552%	$90.1662	$90.17	$90.15	$90.20
Purchase #6	$93.25	7.624%	$100.3594	$100.36	$100.35	$100.40
Purchase #7	$113.29	11.697%	$126.5415	$126.54	$126.55	$126.50
7 purchase totals =	$689.22		$753.8536	$753.86	$753.85	$754.00