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	$51.42	5.769%	$54.3864	$54.39	$54.40	$54.40
Purchase #2	$42.63	7.543%	$45.8456	$45.85	$45.85	$45.80
Purchase #3	$179.65	6.441%	$191.2213	$191.22	$191.20	$191.20
Purchase #4	$189.56	10.463%	$209.3937	$209.39	$209.40	$209.40
Purchase #5	$78.90	5.628%	$83.3405	$83.34	$83.35	$83.30
Purchase #6	$127.54	6.251%	$135.5125	$135.51	$135.50	$135.50
Purchase #7	$213.60	11.245%	$237.6193	$237.62	$237.60	$237.60
7 purchase totals =	$883.30		$957.3193	$957.32	$957.30	$957.20