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	$97.51	6.473%	$103.8218	$103.82	$103.80	$103.80
Purchase #2	$231.34	5.167%	$243.2933	$243.29	$243.30	$243.30
Purchase #3	$188.87	4.103%	$196.6193	$196.62	$196.60	$196.60
Purchase #4	$86.39	10.839%	$95.7538	$95.75	$95.75	$95.80
Purchase #5	$209.47	9.266%	$228.8795	$228.88	$228.90	$228.90
Purchase #6	$84.69	6.416%	$90.1237	$90.12	$90.10	$90.10
Purchase #7	$204.58	7.600%	$220.1281	$220.13	$220.15	$220.10
7 purchase totals =	$1,102.85		$1,178.6195	$1,178.61	$1,178.60	$1,178.60