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	$51.98	13.271%	$58.8783	$58.88	$58.90	$58.90
Purchase #2	$189.32	3.824%	$196.5596	$196.56	$196.55	$196.60
Purchase #3	$170.77	5.184%	$179.6227	$179.62	$179.60	$179.60
Purchase #4	$147.54	7.678%	$158.8681	$158.87	$158.85	$158.90
Purchase #5	$81.62	10.755%	$90.3982	$90.40	$90.40	$90.40
Purchase #6	$35.63	5.349%	$37.5358	$37.54	$37.55	$37.50
Purchase #7	$188.50	9.189%	$205.8213	$205.82	$205.80	$205.80
7 purchase totals =	$865.36		$927.6840	$927.69	$927.65	$927.70