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	$26.36	6.792%	$28.1504	$28.15	$28.15	$28.20
Purchase #2	$200.45	11.580%	$223.6621	$223.66	$223.65	$223.70
Purchase #3	$72.32	5.722%	$76.4582	$76.46	$76.45	$76.50
Purchase #4	$112.74	9.803%	$123.7919	$123.79	$123.80	$123.80
Purchase #5	$121.33	3.798%	$125.9381	$125.94	$125.95	$125.90
Purchase #6	$153.34	10.793%	$169.89	$169.89	$169.90	$169.90
Purchase #7	$210.83	4.772%	$220.8908	$220.89	$220.90	$220.90
7 purchase totals =	$897.37		$968.7815	$968.78	$968.80	$968.90