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	$133.48	11.856%	$149.3054	$149.31	$149.30	$149.30
Purchase #2	$66.29	9.205%	$72.392	$72.39	$72.40	$72.40
Purchase #3	$171.75	13.784%	$195.424	$195.42	$195.40	$195.40
Purchase #4	$98.48	7.161%	$105.5322	$105.53	$105.55	$105.50
Purchase #5	$185.31	10.617%	$204.9844	$204.98	$205.00	$205.00
Purchase #6	$41.61	9.669%	$45.6333	$45.63	$45.65	$45.60
Purchase #7	$13.78	10.749%	$15.2612	$15.26	$15.25	$15.30
7 purchase totals =	$710.70		$788.5325	$788.52	$788.55	$788.50