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	$30.89	7.365%	$33.165	$33.17	$33.15	$33.20
Purchase #2	$100.93	11.761%	$112.8004	$112.80	$112.80	$112.80
Purchase #3	$221.47	11.275%	$246.4407	$246.44	$246.45	$246.40
Purchase #4	$100.42	5.321%	$105.7633	$105.76	$105.75	$105.80
Purchase #5	$23.89	11.438%	$26.6225	$26.62	$26.60	$26.60
Purchase #6	$180.28	11.370%	$200.7778	$200.78	$200.80	$200.80
Purchase #7	$234.83	5.626%	$248.0415	$248.04	$248.05	$248.00
7 purchase totals =	$892.71		$973.6112	$973.61	$973.60	$973.60