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	$185.76	9.785%	$203.9366	$203.94	$203.95	$203.90
Purchase #2	$170.33	10.833%	$188.7818	$188.78	$188.80	$188.80
Purchase #3	$105.85	12.259%	$118.8262	$118.83	$118.85	$118.80
Purchase #4	$33.57	5.553%	$35.4341	$35.43	$35.45	$35.40
Purchase #5	$49.81	13.431%	$56.5	$56.50	$56.50	$56.50
Purchase #6	$239.80	12.139%	$268.9093	$268.91	$268.90	$268.90
Purchase #7	$69.44	4.523%	$72.5808	$72.58	$72.60	$72.60
7 purchase totals =	$854.56		$944.9688	$944.97	$945.05	$944.90