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	$96.95	12.345%	$108.9185	$108.92	$108.90	$108.90
Purchase #2	$127.31	13.448%	$144.4306	$144.43	$144.45	$144.40
Purchase #3	$204.55	13.560%	$232.287	$232.29	$232.30	$232.30
Purchase #4	$28.62	11.503%	$31.9122	$31.91	$31.90	$31.90
Purchase #5	$103.72	12.499%	$116.684	$116.68	$116.70	$116.70
Purchase #6	$76.68	11.237%	$85.2965	$85.30	$85.30	$85.30
Purchase #7	$59.94	8.128%	$64.8119	$64.81	$64.80	$64.80
7 purchase totals =	$697.77		$784.3407	$784.34	$784.35	$784.30