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	$136.44	6.604%	$145.4505	$145.45	$145.45	$145.50
Purchase #2	$250.50	6.305%	$266.294	$266.29	$266.30	$266.30
Purchase #3	$129.98	3.188%	$134.1238	$134.12	$134.10	$134.10
Purchase #4	$88.62	7.639%	$95.3897	$95.39	$95.40	$95.40
Purchase #5	$129.72	10.643%	$143.5261	$143.53	$143.55	$143.50
Purchase #6	$244.71	10.155%	$269.5603	$269.56	$269.55	$269.60
Purchase #7	$37.34	3.183%	$38.5285	$38.53	$38.55	$38.50
7 purchase totals =	$1,017.31		$1,092.8729	$1,092.87	$1,092.90	$1,092.90