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	$240.55	11.784%	$268.8964	$268.90	$268.90	$268.90
Purchase #2	$54.84	4.633%	$57.3807	$57.38	$57.40	$57.40
Purchase #3	$242.50	8.365%	$262.7851	$262.79	$262.80	$262.80
Purchase #4	$141.27	10.508%	$156.1147	$156.11	$156.10	$156.10
Purchase #5	$172.36	3.799%	$178.908	$178.91	$178.90	$178.90
Purchase #6	$35.87	3.176%	$37.0092	$37.01	$37.00	$37.00
Purchase #7	$49.72	11.517%	$55.4463	$55.45	$55.45	$55.40
7 purchase totals =	$937.11		$1,016.5404	$1,016.55	$1,016.55	$1,016.50