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	$166.48	8.509%	$180.6458	$180.65	$180.65	$180.60
Purchase #2	$142.53	9.639%	$156.2685	$156.27	$156.25	$156.30
Purchase #3	$146.75	4.190%	$152.8988	$152.90	$152.90	$152.90
Purchase #4	$162.71	8.795%	$177.0203	$177.02	$177.00	$177.00
Purchase #5	$235.72	6.103%	$250.106	$250.11	$250.10	$250.10
Purchase #6	$162.44	6.695%	$173.3154	$173.32	$173.30	$173.30
Purchase #7	$68.72	4.677%	$71.934	$71.93	$71.95	$71.90
7 purchase totals =	$1,085.35		$1,162.1888	$1,162.20	$1,162.15	$1,162.10