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	$92.66	12.641%	$104.3732	$104.37	$104.35	$104.40
Purchase #2	$249.39	11.564%	$278.2295	$278.23	$278.25	$278.20
Purchase #3	$198.28	11.679%	$221.4371	$221.44	$221.45	$221.40
Purchase #4	$135.42	4.688%	$141.7685	$141.77	$141.75	$141.80
Purchase #5	$42.59	6.187%	$45.225	$45.23	$45.25	$45.20
Purchase #6	$101.47	9.791%	$111.4049	$111.40	$111.40	$111.40
Purchase #7	$113.63	4.516%	$118.7615	$118.76	$118.75	$118.80
7 purchase totals =	$933.44		$1,021.1997	$1,021.20	$1,021.20	$1,021.20