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	$152.82	9.130%	$166.7725	$166.77	$166.75	$166.80
Purchase #2	$215.50	3.846%	$223.7881	$223.79	$223.80	$223.80
Purchase #3	$70.40	10.441%	$77.7505	$77.75	$77.75	$77.80
Purchase #4	$167.70	11.557%	$187.0811	$187.08	$187.10	$187.10
Purchase #5	$158.94	13.566%	$180.5018	$180.50	$180.50	$180.50
Purchase #6	$95.66	8.773%	$104.0523	$104.05	$104.05	$104.10
Purchase #7	$56.69	9.252%	$61.935	$61.94	$61.95	$61.90
7 purchase totals =	$917.71		$1,001.8813	$1,001.88	$1,001.90	$1,002.00