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	$211.60	7.518%	$227.5081	$227.51	$227.50	$227.50
Purchase #2	$82.96	9.625%	$90.9449	$90.94	$90.95	$90.90
Purchase #3	$32.88	13.777%	$37.4099	$37.41	$37.40	$37.40
Purchase #4	$71.87	3.370%	$74.292	$74.29	$74.30	$74.30
Purchase #5	$125.90	9.184%	$137.4627	$137.46	$137.45	$137.50
Purchase #6	$135.76	4.252%	$141.5325	$141.53	$141.55	$141.50
Purchase #7	$116.53	11.373%	$129.783	$129.78	$129.80	$129.80
7 purchase totals =	$777.50		$838.9331	$838.92	$838.95	$838.90