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	$234.63	6.308%	$249.4305	$249.43	$249.45	$249.40
Purchase #2	$211.75	13.786%	$240.9419	$240.94	$240.95	$240.90
Purchase #3	$71.28	9.659%	$78.1649	$78.16	$78.15	$78.20
Purchase #4	$31.94	7.770%	$34.4217	$34.42	$34.40	$34.40
Purchase #5	$48.37	7.282%	$51.8923	$51.89	$51.90	$51.90
Purchase #6	$35.85	13.566%	$40.7134	$40.71	$40.70	$40.70
Purchase #7	$77.95	6.400%	$82.9388	$82.94	$82.95	$82.90
7 purchase totals =	$711.77		$778.5035	$778.49	$778.50	$778.40