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	$233.34	11.394%	$259.9268	$259.93	$259.95	$259.90
Purchase #2	$118.82	9.198%	$129.7491	$129.75	$129.75	$129.70
Purchase #3	$53.81	3.541%	$55.7154	$55.72	$55.70	$55.70
Purchase #4	$236.52	10.735%	$261.9104	$261.91	$261.90	$261.90
Purchase #5	$104.28	7.822%	$112.4368	$112.44	$112.45	$112.40
Purchase #6	$105.81	13.809%	$120.4213	$120.42	$120.40	$120.40
Purchase #7	$85.30	5.660%	$90.128	$90.13	$90.15	$90.10
7 purchase totals =	$937.88		$1,030.2878	$1,030.30	$1,030.30	$1,030.10