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	$67.79	8.318%	$73.4288	$73.43	$73.45	$73.40
Purchase #2	$89.47	13.232%	$101.3087	$101.31	$101.30	$101.30
Purchase #3	$132.55	8.149%	$143.3515	$143.35	$143.35	$143.40
Purchase #4	$174.59	8.726%	$189.8247	$189.82	$189.80	$189.80
Purchase #5	$10.93	6.666%	$11.6586	$11.66	$11.65	$11.70
Purchase #6	$52.80	4.586%	$55.2214	$55.22	$55.20	$55.20
Purchase #7	$65.59	9.378%	$71.741	$71.74	$71.75	$71.70
7 purchase totals =	$593.72		$646.5347	$646.53	$646.50	$646.50