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	$171.90	11.660%	$191.9435	$191.94	$191.95	$191.90
Purchase #2	$167.72	3.310%	$173.2715	$173.27	$173.25	$173.30
Purchase #3	$160.83	13.232%	$182.111	$182.11	$182.10	$182.10
Purchase #4	$93.92	10.171%	$103.4726	$103.47	$103.45	$103.50
Purchase #5	$92.73	8.468%	$100.5824	$100.58	$100.60	$100.60
Purchase #6	$100.35	12.558%	$112.952	$112.95	$112.95	$113.00
Purchase #7	$50.37	10.132%	$55.4735	$55.47	$55.45	$55.50
7 purchase totals =	$837.82		$919.8065	$919.79	$919.75	$919.90