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	$40.77	11.555%	$45.481	$45.48	$45.50	$45.50
Purchase #2	$148.26	4.724%	$155.2638	$155.26	$155.25	$155.30
Purchase #3	$192.66	13.287%	$218.2587	$218.26	$218.25	$218.30
Purchase #4	$80.70	5.733%	$85.3265	$85.33	$85.35	$85.30
Purchase #5	$147.84	11.660%	$165.0781	$165.08	$165.10	$165.10
Purchase #6	$218.88	3.388%	$226.2957	$226.30	$226.30	$226.30
Purchase #7	$191.27	12.492%	$215.1634	$215.16	$215.15	$215.20
7 purchase totals =	$1,020.38		$1,110.8672	$1,110.87	$1,110.90	$1,111.00