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	$127.89	5.178%	$134.5121	$134.51	$134.50	$134.50
Purchase #2	$85.96	5.811%	$90.9551	$90.96	$90.95	$91.00
Purchase #3	$249.44	11.718%	$278.6694	$278.67	$278.65	$278.70
Purchase #4	$205.52	7.668%	$221.2793	$221.28	$221.30	$221.30
Purchase #5	$175.52	10.308%	$193.6126	$193.61	$193.60	$193.60
Purchase #6	$67.82	12.323%	$76.1775	$76.18	$76.20	$76.20
Purchase #7	$91.48	10.731%	$101.2967	$101.30	$101.30	$101.30
7 purchase totals =	$1,003.63		$1,096.5027	$1,096.51	$1,096.50	$1,096.60