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	$149.89	10.728%	$165.9702	$165.97	$165.95	$166.00
Purchase #2	$69.75	6.780%	$74.4791	$74.48	$74.50	$74.50
Purchase #3	$121.97	6.165%	$129.4895	$129.49	$129.50	$129.50
Purchase #4	$142.60	9.457%	$156.0857	$156.09	$156.10	$156.10
Purchase #5	$141.80	6.828%	$151.4821	$151.48	$151.50	$151.50
Purchase #6	$80.85	11.545%	$90.1841	$90.18	$90.20	$90.20
Purchase #7	$232.37	7.804%	$250.5042	$250.50	$250.50	$250.50
7 purchase totals =	$939.23		$1,018.1949	$1,018.19	$1,018.25	$1,018.30