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	$55.42	8.431%	$60.0925	$60.09	$60.10	$60.10
Purchase #2	$105.74	11.713%	$118.1253	$118.13	$118.15	$118.10
Purchase #3	$94.69	6.227%	$100.5863	$100.59	$100.60	$100.60
Purchase #4	$103.32	11.281%	$114.9755	$114.98	$115.00	$115.00
Purchase #5	$59.77	12.274%	$67.1062	$67.11	$67.10	$67.10
Purchase #6	$248.51	8.712%	$270.1602	$270.16	$270.15	$270.20
Purchase #7	$165.65	6.550%	$176.5001	$176.50	$176.50	$176.50
7 purchase totals =	$833.10		$907.5461	$907.56	$907.60	$907.60