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	$223.83	6.785%	$239.0169	$239.02	$239.00	$239.00
Purchase #2	$59.56	4.546%	$62.2676	$62.27	$62.25	$62.30
Purchase #3	$42.56	5.206%	$44.7757	$44.78	$44.80	$44.80
Purchase #4	$248.60	5.689%	$262.7429	$262.74	$262.75	$262.70
Purchase #5	$84.98	5.727%	$89.8468	$89.85	$89.85	$89.80
Purchase #6	$208.72	12.241%	$234.2694	$234.27	$234.25	$234.30
Purchase #7	$41.98	7.631%	$45.1835	$45.18	$45.20	$45.20
7 purchase totals =	$910.23		$978.1028	$978.11	$978.10	$978.10