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	$141.67	4.697%	$148.3242	$148.32	$148.30	$148.30
Purchase #2	$189.83	8.694%	$206.3338	$206.33	$206.35	$206.30
Purchase #3	$180.72	12.403%	$203.1347	$203.13	$203.15	$203.10
Purchase #4	$89.35	5.298%	$94.0838	$94.08	$94.10	$94.10
Purchase #5	$247.62	12.738%	$279.1618	$279.16	$279.15	$279.20
Purchase #6	$187.48	4.804%	$196.4865	$196.49	$196.50	$196.50
Purchase #7	$51.46	3.520%	$53.2714	$53.27	$53.25	$53.30
7 purchase totals =	$1,088.13		$1,180.7962	$1,180.78	$1,180.80	$1,180.80