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	$221.42	12.667%	$249.4673	$249.47	$249.45	$249.50
Purchase #2	$102.41	4.294%	$106.8075	$106.81	$106.80	$106.80
Purchase #3	$142.95	7.783%	$154.0758	$154.08	$154.10	$154.10
Purchase #4	$133.26	4.691%	$139.5112	$139.51	$139.50	$139.50
Purchase #5	$72.74	4.191%	$75.7885	$75.79	$75.80	$75.80
Purchase #6	$123.37	7.385%	$132.4809	$132.48	$132.50	$132.50
Purchase #7	$172.49	13.767%	$196.2367	$196.24	$196.25	$196.20
7 purchase totals =	$968.64		$1,054.3679	$1,054.38	$1,054.40	$1,054.40