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	$131.32	4.238%	$136.8853	$136.89	$136.90	$136.90
Purchase #2	$159.94	8.106%	$172.9047	$172.90	$172.90	$172.90
Purchase #3	$96.27	3.234%	$99.3834	$99.38	$99.40	$99.40
Purchase #4	$200.74	3.825%	$208.4183	$208.42	$208.40	$208.40
Purchase #5	$28.79	4.231%	$30.0081	$30.01	$30.00	$30.00
Purchase #6	$87.88	8.590%	$95.4289	$95.43	$95.45	$95.40
Purchase #7	$123.38	5.580%	$130.2646	$130.26	$130.25	$130.30
7 purchase totals =	$828.32		$873.2933	$873.29	$873.30	$873.30