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	$107.69	12.461%	$121.1093	$121.11	$121.10	$121.10
Purchase #2	$185.56	6.731%	$198.05	$198.05	$198.05	$198.10
Purchase #3	$77.57	10.233%	$85.5077	$85.51	$85.50	$85.50
Purchase #4	$162.94	6.136%	$172.938	$172.94	$172.95	$172.90
Purchase #5	$169.97	9.218%	$185.6378	$185.64	$185.65	$185.60
Purchase #6	$6.29	9.235%	$6.8709	$6.87	$6.85	$6.90
Purchase #7	$100.67	8.544%	$109.2712	$109.27	$109.25	$109.30
7 purchase totals =	$810.69		$879.3849	$879.39	$879.35	$879.40