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	$249.88	8.634%	$271.4546	$271.45	$271.45	$271.50
Purchase #2	$138.25	3.230%	$142.7155	$142.72	$142.70	$142.70
Purchase #3	$65.60	8.395%	$71.1071	$71.11	$71.10	$71.10
Purchase #4	$158.54	5.264%	$166.8855	$166.89	$166.90	$166.90
Purchase #5	$12.41	12.354%	$13.9431	$13.94	$13.95	$13.90
Purchase #6	$35.83	13.664%	$40.7258	$40.73	$40.75	$40.70
Purchase #7	$68.45	13.588%	$77.751	$77.75	$77.75	$77.80
7 purchase totals =	$728.96		$784.5826	$784.59	$784.60	$784.60