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	$133.87	7.307%	$143.6519	$143.65	$143.65	$143.70
Purchase #2	$51.81	12.823%	$58.4536	$58.45	$58.45	$58.50
Purchase #3	$130.27	8.578%	$141.4446	$141.44	$141.45	$141.40
Purchase #4	$180.31	10.612%	$199.4445	$199.44	$199.45	$199.40
Purchase #5	$248.64	7.336%	$266.8802	$266.88	$266.90	$266.90
Purchase #6	$41.97	3.144%	$43.2895	$43.29	$43.30	$43.30
Purchase #7	$52.81	12.555%	$59.4403	$59.44	$59.45	$59.40
7 purchase totals =	$839.68		$912.6046	$912.59	$912.65	$912.60