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	$88.35	13.466%	$100.2472	$100.25	$100.25	$100.20
Purchase #2	$34.88	5.110%	$36.6624	$36.66	$36.65	$36.70
Purchase #3	$24.31	8.839%	$26.4588	$26.46	$26.45	$26.50
Purchase #4	$175.61	12.745%	$197.9915	$197.99	$198.00	$198.00
Purchase #5	$182.42	7.617%	$196.3149	$196.31	$196.30	$196.30
Purchase #6	$250.90	5.364%	$264.3583	$264.36	$264.35	$264.40
Purchase #7	$80.43	6.343%	$85.5317	$85.53	$85.55	$85.50
7 purchase totals =	$836.90		$907.5648	$907.56	$907.55	$907.60