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	$43.79	10.705%	$48.4777	$48.48	$48.50	$48.50
Purchase #2	$114.79	8.417%	$124.4519	$124.45	$124.45	$124.50
Purchase #3	$83.53	6.421%	$88.8935	$88.89	$88.90	$88.90
Purchase #4	$74.86	5.117%	$78.6906	$78.69	$78.70	$78.70
Purchase #5	$86.88	8.820%	$94.5428	$94.54	$94.55	$94.50
Purchase #6	$245.87	13.586%	$279.2739	$279.27	$279.25	$279.30
Purchase #7	$146.44	4.316%	$152.7604	$152.76	$152.75	$152.80
7 purchase totals =	$796.16		$867.0908	$867.08	$867.10	$867.20