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	$136.46	11.776%	$152.5295	$152.53	$152.55	$152.50
Purchase #2	$98.47	4.452%	$102.8539	$102.85	$102.85	$102.90
Purchase #3	$24.70	12.874%	$27.8799	$27.88	$27.90	$27.90
Purchase #4	$211.66	10.157%	$233.1583	$233.16	$233.15	$233.20
Purchase #5	$58.40	11.586%	$65.1662	$65.17	$65.15	$65.20
Purchase #6	$72.51	7.359%	$77.846	$77.85	$77.85	$77.80
Purchase #7	$123.29	4.456%	$128.7838	$128.78	$128.80	$128.80
7 purchase totals =	$725.49		$788.2176	$788.22	$788.25	$788.30