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	$45.73	5.245%	$48.1285	$48.13	$48.15	$48.10
Purchase #2	$35.78	13.586%	$40.6411	$40.64	$40.65	$40.60
Purchase #3	$131.71	13.805%	$149.8926	$149.89	$149.90	$149.90
Purchase #4	$31.45	8.163%	$34.0173	$34.02	$34.00	$34.00
Purchase #5	$35.83	8.465%	$38.863	$38.86	$38.85	$38.90
Purchase #6	$198.40	3.456%	$205.2567	$205.26	$205.25	$205.30
Purchase #7	$75.99	8.314%	$82.3078	$82.31	$82.30	$82.30
7 purchase totals =	$554.89		$599.1070	$599.11	$599.10	$599.10