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	$27.33	12.492%	$30.7441	$30.74	$30.75	$30.70
Purchase #2	$53.79	4.855%	$56.4015	$56.40	$56.40	$56.40
Purchase #3	$207.34	7.764%	$223.4379	$223.44	$223.45	$223.40
Purchase #4	$59.69	13.568%	$67.7887	$67.79	$67.80	$67.80
Purchase #5	$243.82	13.429%	$276.5626	$276.56	$276.55	$276.60
Purchase #6	$128.78	10.718%	$142.5826	$142.58	$142.60	$142.60
Purchase #7	$235.67	11.176%	$262.0085	$262.01	$262.00	$262.00
7 purchase totals =	$956.42		$1,059.5259	$1,059.52	$1,059.55	$1,059.50