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	$80.64	10.729%	$89.2919	$89.29	$89.30	$89.30
Purchase #2	$92.51	4.658%	$96.8191	$96.82	$96.80	$96.80
Purchase #3	$31.66	12.152%	$35.5073	$35.51	$35.50	$35.50
Purchase #4	$157.43	6.534%	$167.7165	$167.72	$167.70	$167.70
Purchase #5	$129.26	10.451%	$142.769	$142.77	$142.75	$142.80
Purchase #6	$31.34	10.590%	$34.6589	$34.66	$34.65	$34.70
Purchase #7	$223.70	11.690%	$249.8505	$249.85	$249.85	$249.90
7 purchase totals =	$746.54		$816.6132	$816.62	$816.55	$816.70