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	$85.82	7.776%	$92.4934	$92.49	$92.50	$92.50
Purchase #2	$149.60	11.647%	$167.0239	$167.02	$167.00	$167.00
Purchase #3	$77.87	13.854%	$88.6581	$88.66	$88.65	$88.70
Purchase #4	$192.27	5.615%	$203.066	$203.07	$203.05	$203.10
Purchase #5	$142.31	4.531%	$148.7581	$148.76	$148.75	$148.80
Purchase #6	$147.42	3.632%	$152.7743	$152.77	$152.75	$152.80
Purchase #7	$206.49	13.302%	$233.9573	$233.96	$233.95	$234.00
7 purchase totals =	$1,001.78		$1,086.7311	$1,086.73	$1,086.65	$1,086.90