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	$217.77	9.393%	$238.2251	$238.23	$238.25	$238.20
Purchase #2	$118.36	4.615%	$123.8223	$123.82	$123.80	$123.80
Purchase #3	$66.71	8.164%	$72.1562	$72.16	$72.15	$72.20
Purchase #4	$214.56	8.211%	$232.1775	$232.18	$232.20	$232.20
Purchase #5	$120.70	6.325%	$128.3343	$128.33	$128.35	$128.30
Purchase #6	$99.81	4.435%	$104.2366	$104.24	$104.25	$104.20
Purchase #7	$166.51	13.872%	$189.6083	$189.61	$189.60	$189.60
7 purchase totals =	$1,004.42		$1,088.5603	$1,088.57	$1,088.60	$1,088.50