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	$244.72	12.641%	$275.6551	$275.66	$275.65	$275.70
Purchase #2	$248.66	6.488%	$264.7931	$264.79	$264.80	$264.80
Purchase #3	$49.77	4.355%	$51.9375	$51.94	$51.95	$51.90
Purchase #4	$37.82	11.246%	$42.0732	$42.07	$42.05	$42.10
Purchase #5	$194.83	5.399%	$205.3489	$205.35	$205.35	$205.30
Purchase #6	$206.72	4.790%	$216.6219	$216.62	$216.60	$216.60
Purchase #7	$18.92	8.199%	$20.4713	$20.47	$20.45	$20.50
7 purchase totals =	$1,001.44		$1,076.9010	$1,076.90	$1,076.85	$1,076.90