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	$123.53	13.129%	$139.7483	$139.75	$139.75	$139.70
Purchase #2	$38.75	7.173%	$41.5295	$41.53	$41.55	$41.50
Purchase #3	$52.27	13.223%	$59.1817	$59.18	$59.20	$59.20
Purchase #4	$222.56	5.109%	$233.9306	$233.93	$233.95	$233.90
Purchase #5	$16.74	5.417%	$17.6468	$17.65	$17.65	$17.60
Purchase #6	$42.76	5.330%	$45.0391	$45.04	$45.05	$45.00
Purchase #7	$56.97	4.787%	$59.6972	$59.70	$59.70	$59.70
7 purchase totals =	$553.58		$596.7732	$596.78	$596.85	$596.60