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	$89.46	12.103%	$100.2873	$100.29	$100.30	$100.30
Purchase #2	$26.51	7.422%	$28.4776	$28.48	$28.50	$28.50
Purchase #3	$73.49	7.842%	$79.2531	$79.25	$79.25	$79.30
Purchase #4	$157.41	11.544%	$175.5814	$175.58	$175.60	$175.60
Purchase #5	$115.64	3.200%	$119.3405	$119.34	$119.35	$119.30
Purchase #6	$95.76	9.602%	$104.9549	$104.95	$104.95	$105.00
Purchase #7	$109.70	3.454%	$113.489	$113.49	$113.50	$113.50
7 purchase totals =	$667.97		$721.3838	$721.38	$721.45	$721.50