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	$222.91	8.615%	$242.1137	$242.11	$242.10	$242.10
Purchase #2	$85.77	4.410%	$89.5525	$89.55	$89.55	$89.60
Purchase #3	$196.88	4.719%	$206.1708	$206.17	$206.15	$206.20
Purchase #4	$64.55	3.573%	$66.8564	$66.86	$66.85	$66.90
Purchase #5	$66.62	9.397%	$72.8803	$72.88	$72.90	$72.90
Purchase #6	$29.55	8.361%	$32.0207	$32.02	$32.00	$32.00
Purchase #7	$199.94	3.500%	$206.9379	$206.94	$206.95	$206.90
7 purchase totals =	$866.22		$916.5323	$916.53	$916.50	$916.60