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	$128.45	7.549%	$138.1467	$138.15	$138.15	$138.10
Purchase #2	$170.68	12.131%	$191.3852	$191.39	$191.40	$191.40
Purchase #3	$63.47	12.719%	$71.5427	$71.54	$71.55	$71.50
Purchase #4	$38.84	6.159%	$41.2322	$41.23	$41.25	$41.20
Purchase #5	$85.51	13.178%	$96.7785	$96.78	$96.80	$96.80
Purchase #6	$51.72	8.295%	$56.0102	$56.01	$56.00	$56.00
Purchase #7	$133.40	5.869%	$141.2292	$141.23	$141.25	$141.20
7 purchase totals =	$672.07		$736.3247	$736.33	$736.40	$736.20