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	$35.87	5.501%	$37.8432	$37.84	$37.85	$37.80
Purchase #2	$249.85	7.585%	$268.8011	$268.80	$268.80	$268.80
Purchase #3	$19.62	4.725%	$20.547	$20.55	$20.55	$20.50
Purchase #4	$216.98	12.591%	$244.3	$244.30	$244.30	$244.30
Purchase #5	$69.32	13.180%	$78.4564	$78.46	$78.45	$78.50
Purchase #6	$32.99	8.817%	$35.8987	$35.90	$35.90	$35.90
Purchase #7	$169.81	5.796%	$179.6522	$179.65	$179.65	$179.70
7 purchase totals =	$794.44		$865.4986	$865.50	$865.50	$865.50