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	$21.78	11.387%	$24.2601	$24.26	$24.25	$24.30
Purchase #2	$97.73	7.531%	$105.09	$105.09	$105.10	$105.10
Purchase #3	$167.82	7.620%	$180.6079	$180.61	$180.60	$180.60
Purchase #4	$247.29	5.234%	$260.2332	$260.23	$260.25	$260.20
Purchase #5	$49.50	5.681%	$52.3121	$52.31	$52.30	$52.30
Purchase #6	$133.64	3.793%	$138.709	$138.71	$138.70	$138.70
Purchase #7	$84.78	6.752%	$90.5043	$90.50	$90.50	$90.50
7 purchase totals =	$802.54		$851.7166	$851.71	$851.70	$851.70