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	$32.41	3.726%	$33.6176	$33.62	$33.60	$33.60
Purchase #2	$31.33	3.839%	$32.5328	$32.53	$32.55	$32.50
Purchase #3	$143.87	10.132%	$158.4469	$158.45	$158.45	$158.40
Purchase #4	$30.71	5.828%	$32.4998	$32.50	$32.50	$32.50
Purchase #5	$162.69	5.134%	$171.0425	$171.04	$171.05	$171.00
Purchase #6	$50.94	9.247%	$55.6504	$55.65	$55.65	$55.70
Purchase #7	$34.56	12.806%	$38.9858	$38.99	$39.00	$39.00
7 purchase totals =	$486.51		$522.7758	$522.78	$522.80	$522.70