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	$109.86	10.790%	$121.7139	$121.71	$121.70	$121.70
Purchase #2	$137.31	7.692%	$147.8719	$147.87	$147.85	$147.90
Purchase #3	$215.97	8.358%	$234.0208	$234.02	$234.00	$234.00
Purchase #4	$162.88	13.171%	$184.3329	$184.33	$184.35	$184.30
Purchase #5	$52.27	7.109%	$55.9859	$55.99	$56.00	$56.00
Purchase #6	$80.55	11.862%	$90.1048	$90.10	$90.10	$90.10
Purchase #7	$79.57	7.478%	$85.5202	$85.52	$85.50	$85.50
7 purchase totals =	$838.41		$919.5504	$919.54	$919.50	$919.50