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	$123.27	6.665%	$131.4859	$131.49	$131.50	$131.50
Purchase #2	$69.78	11.656%	$77.9136	$77.91	$77.90	$77.90
Purchase #3	$192.65	8.250%	$208.5436	$208.54	$208.55	$208.50
Purchase #4	$13.98	4.130%	$14.5574	$14.56	$14.55	$14.60
Purchase #5	$220.51	7.375%	$236.7726	$236.77	$236.75	$236.80
Purchase #6	$30.63	5.489%	$32.3113	$32.31	$32.30	$32.30
Purchase #7	$34.69	7.306%	$37.2245	$37.22	$37.20	$37.20
7 purchase totals =	$685.51		$738.8089	$738.80	$738.75	$738.80