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	$82.52	13.147%	$93.3689	$93.37	$93.35	$93.40
Purchase #2	$137.62	3.577%	$142.5427	$142.54	$142.55	$142.50
Purchase #3	$58.79	10.830%	$65.157	$65.16	$65.15	$65.20
Purchase #4	$79.55	10.273%	$87.7222	$87.72	$87.70	$87.70
Purchase #5	$249.38	13.444%	$282.9066	$282.91	$282.90	$282.90
Purchase #6	$60.66	10.317%	$66.9183	$66.92	$66.90	$66.90
Purchase #7	$74.52	10.197%	$82.1188	$82.12	$82.10	$82.10
7 purchase totals =	$743.04		$820.7345	$820.74	$820.65	$820.70