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	$170.73	10.353%	$188.4057	$188.41	$188.40	$188.40
Purchase #2	$58.69	7.587%	$63.1428	$63.14	$63.15	$63.10
Purchase #3	$33.45	10.698%	$37.0285	$37.03	$37.05	$37.00
Purchase #4	$39.47	6.147%	$41.8962	$41.90	$41.90	$41.90
Purchase #5	$112.80	10.207%	$124.3135	$124.31	$124.30	$124.30
Purchase #6	$175.60	12.156%	$196.9459	$196.95	$196.95	$196.90
Purchase #7	$25.87	9.130%	$28.2319	$28.23	$28.25	$28.20
7 purchase totals =	$616.61		$679.9645	$679.97	$680.00	$679.80