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	$132.73	11.319%	$147.7537	$147.75	$147.75	$147.80
Purchase #2	$42.71	7.223%	$45.7949	$45.79	$45.80	$45.80
Purchase #3	$43.31	5.872%	$45.8532	$45.85	$45.85	$45.90
Purchase #4	$145.77	5.530%	$153.8311	$153.83	$153.85	$153.80
Purchase #5	$158.43	3.796%	$164.444	$164.44	$164.45	$164.40
Purchase #6	$68.88	7.434%	$74.0005	$74.00	$74.00	$74.00
Purchase #7	$48.96	7.251%	$52.5101	$52.51	$52.50	$52.50
7 purchase totals =	$640.79		$684.1875	$684.17	$684.20	$684.20