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	$72.33	7.698%	$77.898	$77.90	$77.90	$77.90
Purchase #2	$106.47	4.683%	$111.456	$111.46	$111.45	$111.50
Purchase #3	$196.93	9.818%	$216.2646	$216.26	$216.25	$216.30
Purchase #4	$195.31	9.584%	$214.0285	$214.03	$214.05	$214.00
Purchase #5	$119.85	11.175%	$133.2432	$133.24	$133.25	$133.20
Purchase #6	$119.31	3.812%	$123.8581	$123.86	$123.85	$123.90
Purchase #7	$29.53	12.729%	$33.2889	$33.29	$33.30	$33.30
7 purchase totals =	$839.73		$910.0373	$910.04	$910.05	$910.10