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	$203.75	9.710%	$223.5341	$223.53	$223.55	$223.50
Purchase #2	$83.88	12.107%	$94.0354	$94.04	$94.05	$94.00
Purchase #3	$191.83	8.732%	$208.5806	$208.58	$208.60	$208.60
Purchase #4	$38.31	3.533%	$39.6635	$39.66	$39.65	$39.70
Purchase #5	$6.56	11.437%	$7.3103	$7.31	$7.30	$7.30
Purchase #6	$170.73	13.723%	$194.1593	$194.16	$194.15	$194.20
Purchase #7	$64.69	11.568%	$72.1733	$72.17	$72.15	$72.20
7 purchase totals =	$759.75		$839.4565	$839.45	$839.45	$839.50