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	$34.92	9.438%	$38.2157	$38.22	$38.20	$38.20
Purchase #2	$197.79	6.492%	$210.6305	$210.63	$210.65	$210.60
Purchase #3	$95.94	10.118%	$105.6472	$105.65	$105.65	$105.60
Purchase #4	$160.81	3.746%	$166.8339	$166.83	$166.85	$166.80
Purchase #5	$113.61	5.787%	$120.1846	$120.18	$120.20	$120.20
Purchase #6	$68.51	7.347%	$73.5434	$73.54	$73.55	$73.50
Purchase #7	$93.98	11.850%	$105.1166	$105.12	$105.10	$105.10
7 purchase totals =	$765.56		$820.1719	$820.17	$820.20	$820.00