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	$51.36	8.810%	$55.8848	$55.88	$55.90	$55.90
Purchase #2	$29.38	10.231%	$32.3859	$32.39	$32.40	$32.40
Purchase #3	$135.43	8.427%	$146.8427	$146.84	$146.85	$146.80
Purchase #4	$67.53	13.189%	$76.4365	$76.44	$76.45	$76.40
Purchase #5	$45.47	7.781%	$49.008	$49.01	$49.00	$49.00
Purchase #6	$59.52	8.678%	$64.6851	$64.69	$64.70	$64.70
Purchase #7	$77.54	9.652%	$85.0242	$85.02	$85.00	$85.00
7 purchase totals =	$466.23		$510.2672	$510.27	$510.30	$510.20