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	$206.28	3.628%	$213.7638	$213.76	$213.75	$213.80
Purchase #2	$151.52	8.828%	$164.8962	$164.90	$164.90	$164.90
Purchase #3	$14.79	9.342%	$16.1717	$16.17	$16.15	$16.20
Purchase #4	$113.73	12.489%	$127.9337	$127.93	$127.95	$127.90
Purchase #5	$235.30	7.745%	$253.524	$253.52	$253.50	$253.50
Purchase #6	$65.83	9.560%	$72.1233	$72.12	$72.10	$72.10
Purchase #7	$38.69	5.806%	$40.9363	$40.94	$40.95	$40.90
7 purchase totals =	$826.14		$889.3490	$889.34	$889.30	$889.30