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	$90.76	10.709%	$100.4795	$100.48	$100.50	$100.50
Purchase #2	$72.95	4.272%	$76.0664	$76.07	$76.05	$76.10
Purchase #3	$91.44	4.126%	$95.2128	$95.21	$95.20	$95.20
Purchase #4	$241.83	10.163%	$266.4072	$266.41	$266.40	$266.40
Purchase #5	$240.45	13.721%	$273.4421	$273.44	$273.45	$273.40
Purchase #6	$45.27	3.450%	$46.8318	$46.83	$46.85	$46.80
Purchase #7	$207.25	12.659%	$233.4858	$233.49	$233.50	$233.50
7 purchase totals =	$989.95		$1,091.9256	$1,091.93	$1,091.95	$1,091.90