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	$35.26	6.486%	$37.547	$37.55	$37.55	$37.50
Purchase #2	$44.64	3.842%	$46.3551	$46.36	$46.35	$46.40
Purchase #3	$59.79	9.544%	$65.4964	$65.50	$65.50	$65.50
Purchase #4	$238.60	8.403%	$258.6496	$258.65	$258.65	$258.60
Purchase #5	$47.96	4.716%	$50.2218	$50.22	$50.20	$50.20
Purchase #6	$31.53	4.162%	$32.8423	$32.84	$32.85	$32.80
Purchase #7	$47.66	12.393%	$53.5665	$53.57	$53.55	$53.60
7 purchase totals =	$505.44		$544.6787	$544.69	$544.65	$544.60