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	$103.31	3.868%	$107.306	$107.31	$107.30	$107.30
Purchase #2	$139.32	7.766%	$150.1396	$150.14	$150.15	$150.10
Purchase #3	$88.68	4.362%	$92.5482	$92.55	$92.55	$92.50
Purchase #4	$105.88	12.775%	$119.4062	$119.41	$119.40	$119.40
Purchase #5	$162.96	6.704%	$173.8848	$173.88	$173.90	$173.90
Purchase #6	$126.81	11.517%	$141.4147	$141.41	$141.40	$141.40
Purchase #7	$35.33	11.722%	$39.4714	$39.47	$39.45	$39.50
7 purchase totals =	$762.29		$824.1709	$824.17	$824.15	$824.10