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	$56.27	5.253%	$59.2259	$59.23	$59.25	$59.20
Purchase #2	$123.26	10.105%	$135.7154	$135.72	$135.70	$135.70
Purchase #3	$230.36	12.342%	$258.791	$258.79	$258.80	$258.80
Purchase #4	$246.87	10.323%	$272.3544	$272.35	$272.35	$272.40
Purchase #5	$169.90	10.586%	$187.8856	$187.89	$187.90	$187.90
Purchase #6	$122.90	11.704%	$137.2842	$137.28	$137.30	$137.30
Purchase #7	$60.73	9.251%	$66.3481	$66.35	$66.35	$66.30
7 purchase totals =	$1,010.29		$1,117.6046	$1,117.61	$1,117.65	$1,117.60