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	$159.43	7.186%	$170.8866	$170.89	$170.90	$170.90
Purchase #2	$90.55	10.356%	$99.9274	$99.93	$99.95	$99.90
Purchase #3	$207.74	6.808%	$221.8829	$221.88	$221.90	$221.90
Purchase #4	$167.70	10.380%	$185.1073	$185.11	$185.10	$185.10
Purchase #5	$222.95	8.730%	$242.4135	$242.41	$242.40	$242.40
Purchase #6	$213.58	4.172%	$222.4906	$222.49	$222.50	$222.50
Purchase #7	$137.48	6.245%	$146.0656	$146.07	$146.05	$146.10
7 purchase totals =	$1,199.43		$1,288.7739	$1,288.78	$1,288.80	$1,288.80