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	$52.98	11.598%	$59.1246	$59.12	$59.10	$59.10
Purchase #2	$250.39	9.147%	$273.2932	$273.29	$273.30	$273.30
Purchase #3	$116.90	5.659%	$123.5154	$123.52	$123.50	$123.50
Purchase #4	$245.71	5.223%	$258.5434	$258.54	$258.55	$258.50
Purchase #5	$194.71	9.724%	$213.6436	$213.64	$213.65	$213.60
Purchase #6	$245.73	13.505%	$278.9158	$278.92	$278.90	$278.90
Purchase #7	$9.88	13.736%	$11.2371	$11.24	$11.25	$11.20
7 purchase totals =	$1,116.30		$1,218.2731	$1,218.27	$1,218.25	$1,218.10