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	$82.74	9.821%	$90.8659	$90.87	$90.85	$90.90
Purchase #2	$62.88	6.613%	$67.0383	$67.04	$67.05	$67.00
Purchase #3	$45.54	11.492%	$50.7735	$50.77	$50.75	$50.80
Purchase #4	$85.58	6.247%	$90.9262	$90.93	$90.95	$90.90
Purchase #5	$244.53	8.477%	$265.2588	$265.26	$265.25	$265.30
Purchase #6	$31.86	11.158%	$35.4149	$35.41	$35.40	$35.40
Purchase #7	$240.91	6.265%	$256.003	$256.00	$256.00	$256.00
7 purchase totals =	$794.04		$856.2806	$856.28	$856.25	$856.30