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	$217.41	7.321%	$233.3266	$233.33	$233.35	$233.30
Purchase #2	$108.32	11.642%	$120.9306	$120.93	$120.95	$120.90
Purchase #3	$20.74	3.689%	$21.5051	$21.51	$21.50	$21.50
Purchase #4	$134.59	6.768%	$143.6991	$143.70	$143.70	$143.70
Purchase #5	$20.32	5.417%	$21.4207	$21.42	$21.40	$21.40
Purchase #6	$80.30	8.559%	$87.1729	$87.17	$87.15	$87.20
Purchase #7	$40.37	12.122%	$45.2637	$45.26	$45.25	$45.30
7 purchase totals =	$622.05		$673.3187	$673.32	$673.30	$673.30