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	$105.74	11.734%	$118.1475	$118.15	$118.15	$118.10
Purchase #2	$94.25	10.721%	$104.3545	$104.35	$104.35	$104.40
Purchase #3	$119.54	9.874%	$131.3434	$131.34	$131.35	$131.30
Purchase #4	$40.49	3.190%	$41.7816	$41.78	$41.80	$41.80
Purchase #5	$167.45	10.386%	$184.8414	$184.84	$184.85	$184.80
Purchase #6	$213.68	8.244%	$231.2958	$231.30	$231.30	$231.30
Purchase #7	$85.70	4.204%	$89.3028	$89.30	$89.30	$89.30
7 purchase totals =	$826.85		$901.0670	$901.06	$901.10	$901.00