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	$41.34	3.696%	$42.8679	$42.87	$42.85	$42.90
Purchase #2	$151.58	3.295%	$156.5746	$156.57	$156.55	$156.60
Purchase #3	$73.91	5.676%	$78.1051	$78.11	$78.10	$78.10
Purchase #4	$104.75	3.133%	$108.0318	$108.03	$108.05	$108.00
Purchase #5	$114.55	5.749%	$121.1355	$121.14	$121.15	$121.10
Purchase #6	$153.73	8.164%	$166.2805	$166.28	$166.30	$166.30
Purchase #7	$234.32	11.330%	$260.8685	$260.87	$260.85	$260.90
7 purchase totals =	$874.18		$933.8639	$933.87	$933.85	$933.90