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	$16.89	10.186%	$18.6104	$18.61	$18.60	$18.60
Purchase #2	$140.76	13.678%	$160.0132	$160.01	$160.00	$160.00
Purchase #3	$166.66	4.360%	$173.9264	$173.93	$173.95	$173.90
Purchase #4	$108.34	13.743%	$123.2292	$123.23	$123.25	$123.20
Purchase #5	$193.33	10.158%	$212.9685	$212.97	$212.95	$213.00
Purchase #6	$48.52	12.600%	$54.6335	$54.63	$54.65	$54.60
Purchase #7	$161.49	6.443%	$171.8948	$171.89	$171.90	$171.90
7 purchase totals =	$835.99		$915.2760	$915.27	$915.30	$915.20