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	$247.96	3.639%	$256.9833	$256.98	$257.00	$257.00
Purchase #2	$105.56	10.140%	$116.2638	$116.26	$116.25	$116.30
Purchase #3	$139.69	13.735%	$158.8764	$158.88	$158.90	$158.90
Purchase #4	$109.56	3.544%	$113.4428	$113.44	$113.45	$113.40
Purchase #5	$64.25	10.448%	$70.9628	$70.96	$70.95	$71.00
Purchase #6	$93.72	7.507%	$100.7556	$100.76	$100.75	$100.80
Purchase #7	$213.65	5.378%	$225.1401	$225.14	$225.15	$225.10
7 purchase totals =	$974.39		$1,042.4248	$1,042.42	$1,042.45	$1,042.50