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	$54.60	8.385%	$59.1782	$59.18	$59.20	$59.20
Purchase #2	$11.69	4.484%	$12.2142	$12.21	$12.20	$12.20
Purchase #3	$160.25	13.562%	$181.9831	$181.98	$182.00	$182.00
Purchase #4	$95.51	13.199%	$108.1164	$108.12	$108.10	$108.10
Purchase #5	$131.35	11.443%	$146.3804	$146.38	$146.40	$146.40
Purchase #6	$250.92	10.406%	$277.0307	$277.03	$277.05	$277.00
Purchase #7	$94.67	11.347%	$105.4122	$105.41	$105.40	$105.40
7 purchase totals =	$798.99		$890.3152	$890.31	$890.35	$890.30