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	$94.65	10.266%	$104.3668	$104.37	$104.35	$104.40
Purchase #2	$135.86	10.278%	$149.8237	$149.82	$149.80	$149.80
Purchase #3	$37.94	13.730%	$43.1492	$43.15	$43.15	$43.10
Purchase #4	$134.90	3.148%	$139.1467	$139.15	$139.15	$139.10
Purchase #5	$201.56	4.476%	$210.5818	$210.58	$210.60	$210.60
Purchase #6	$135.56	11.520%	$151.1765	$151.18	$151.20	$151.20
Purchase #7	$95.98	3.273%	$99.1214	$99.12	$99.10	$99.10
7 purchase totals =	$836.45		$897.3661	$897.37	$897.35	$897.30