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	$82.31	6.776%	$87.8873	$87.89	$87.90	$87.90
Purchase #2	$57.54	3.520%	$59.5654	$59.57	$59.55	$59.60
Purchase #3	$224.65	7.796%	$242.1637	$242.16	$242.15	$242.20
Purchase #4	$45.40	10.487%	$50.1611	$50.16	$50.15	$50.20
Purchase #5	$87.66	9.376%	$95.879	$95.88	$95.90	$95.90
Purchase #6	$245.26	12.246%	$275.2945	$275.29	$275.30	$275.30
Purchase #7	$32.32	5.145%	$33.9829	$33.98	$34.00	$34.00
7 purchase totals =	$775.14		$844.9339	$844.93	$844.95	$845.10