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	$151.78	6.290%	$161.327	$161.33	$161.35	$161.30
Purchase #2	$133.72	11.357%	$148.9066	$148.91	$148.90	$148.90
Purchase #3	$88.51	4.390%	$92.3956	$92.40	$92.40	$92.40
Purchase #4	$89.80	12.293%	$100.8391	$100.84	$100.85	$100.80
Purchase #5	$172.86	4.267%	$180.2359	$180.24	$180.25	$180.20
Purchase #6	$95.89	10.480%	$105.9393	$105.94	$105.95	$105.90
Purchase #7	$40.81	3.557%	$42.2616	$42.26	$42.25	$42.30
7 purchase totals =	$773.37		$831.9051	$831.92	$831.95	$831.80