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	$31.25	6.674%	$33.3356	$33.34	$33.35	$33.30
Purchase #2	$94.85	9.225%	$103.5999	$103.60	$103.60	$103.60
Purchase #3	$223.67	13.706%	$254.3262	$254.33	$254.35	$254.30
Purchase #4	$144.64	10.118%	$159.2747	$159.27	$159.25	$159.30
Purchase #5	$11.46	8.530%	$12.4375	$12.44	$12.45	$12.40
Purchase #6	$5.91	8.503%	$6.4125	$6.41	$6.40	$6.40
Purchase #7	$212.89	3.120%	$219.5322	$219.53	$219.55	$219.50
7 purchase totals =	$724.67		$788.9186	$788.92	$788.95	$788.80