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	$166.93	3.332%	$172.4921	$172.49	$172.50	$172.50
Purchase #2	$141.58	8.190%	$153.1754	$153.18	$153.20	$153.20
Purchase #3	$248.90	12.375%	$279.7014	$279.70	$279.70	$279.70
Purchase #4	$33.90	7.464%	$36.4303	$36.43	$36.45	$36.40
Purchase #5	$110.83	8.477%	$120.2251	$120.23	$120.25	$120.20
Purchase #6	$49.36	4.480%	$51.5713	$51.57	$51.55	$51.60
Purchase #7	$80.33	12.671%	$90.5086	$90.51	$90.50	$90.50
7 purchase totals =	$831.83		$904.1042	$904.11	$904.15	$904.10