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	$123.55	10.175%	$136.1212	$136.12	$136.10	$136.10
Purchase #2	$167.45	8.557%	$181.7787	$181.78	$181.80	$181.80
Purchase #3	$41.52	10.519%	$45.8875	$45.89	$45.90	$45.90
Purchase #4	$246.40	12.235%	$276.547	$276.55	$276.55	$276.50
Purchase #5	$247.56	8.147%	$267.7287	$267.73	$267.75	$267.70
Purchase #6	$178.45	3.191%	$184.1443	$184.14	$184.15	$184.10
Purchase #7	$200.74	10.627%	$222.0726	$222.07	$222.05	$222.10
7 purchase totals =	$1,205.67		$1,314.2800	$1,314.28	$1,314.30	$1,314.20