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	$80.31	12.233%	$90.1343	$90.13	$90.15	$90.10
Purchase #2	$175.32	5.870%	$185.6113	$185.61	$185.60	$185.60
Purchase #3	$186.71	4.816%	$195.702	$195.70	$195.70	$195.70
Purchase #4	$234.30	10.255%	$258.3275	$258.33	$258.35	$258.30
Purchase #5	$124.57	12.860%	$140.5897	$140.59	$140.60	$140.60
Purchase #6	$170.86	8.757%	$185.8222	$185.82	$185.80	$185.80
Purchase #7	$180.85	3.312%	$186.8398	$186.84	$186.85	$186.80
7 purchase totals =	$1,152.92		$1,243.0268	$1,243.02	$1,243.05	$1,242.90