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	$21.33	4.779%	$22.3494	$22.35	$22.35	$22.30
Purchase #2	$125.72	4.208%	$131.0103	$131.01	$131.00	$131.00
Purchase #3	$123.52	12.258%	$138.6611	$138.66	$138.65	$138.70
Purchase #4	$55.70	5.156%	$58.5719	$58.57	$58.55	$58.60
Purchase #5	$80.53	12.530%	$90.6204	$90.62	$90.60	$90.60
Purchase #6	$154.28	11.150%	$171.4822	$171.48	$171.50	$171.50
Purchase #7	$215.61	7.199%	$231.1318	$231.13	$231.15	$231.10
7 purchase totals =	$776.69		$843.8271	$843.82	$843.80	$843.80