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	$11.56	12.824%	$13.0425	$13.04	$13.05	$13.00
Purchase #2	$108.78	3.663%	$112.7646	$112.76	$112.75	$112.80
Purchase #3	$213.89	4.657%	$223.8509	$223.85	$223.85	$223.90
Purchase #4	$249.49	11.242%	$277.5377	$277.54	$277.55	$277.50
Purchase #5	$38.46	10.543%	$42.5148	$42.51	$42.50	$42.50
Purchase #6	$121.89	4.485%	$127.3568	$127.36	$127.35	$127.40
Purchase #7	$103.72	11.500%	$115.6478	$115.65	$115.65	$115.60
7 purchase totals =	$847.79		$912.7151	$912.71	$912.70	$912.70