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	$29.53	5.309%	$31.0977	$31.10	$31.10	$31.10
Purchase #2	$198.56	3.211%	$204.9358	$204.94	$204.95	$204.90
Purchase #3	$39.58	13.806%	$45.0444	$45.04	$45.05	$45.00
Purchase #4	$74.34	10.377%	$82.0543	$82.05	$82.05	$82.10
Purchase #5	$19.64	12.459%	$22.0869	$22.09	$22.10	$22.10
Purchase #6	$98.61	12.646%	$111.0802	$111.08	$111.10	$111.10
Purchase #7	$12.80	4.709%	$13.4028	$13.40	$13.40	$13.40
7 purchase totals =	$473.06		$509.7021	$509.70	$509.75	$509.70