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	$92.42	7.748%	$99.5807	$99.58	$99.60	$99.60
Purchase #2	$244.91	11.353%	$272.7146	$272.71	$272.70	$272.70
Purchase #3	$200.31	4.618%	$209.5603	$209.56	$209.55	$209.60
Purchase #4	$149.86	3.347%	$154.8758	$154.88	$154.90	$154.90
Purchase #5	$196.44	8.856%	$213.8367	$213.84	$213.85	$213.80
Purchase #6	$7.34	3.156%	$7.5717	$7.57	$7.55	$7.60
Purchase #7	$37.50	4.202%	$39.0758	$39.08	$39.10	$39.10
7 purchase totals =	$928.78		$997.2156	$997.22	$997.25	$997.30