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	$48.56	11.205%	$54.0011	$54.00	$54.00	$54.00
Purchase #2	$223.43	8.836%	$243.1723	$243.17	$243.15	$243.20
Purchase #3	$247.34	5.102%	$259.9593	$259.96	$259.95	$260.00
Purchase #4	$19.60	8.458%	$21.2578	$21.26	$21.25	$21.30
Purchase #5	$196.81	11.826%	$220.0848	$220.08	$220.10	$220.10
Purchase #6	$82.35	9.137%	$89.8743	$89.87	$89.85	$89.90
Purchase #7	$218.32	7.498%	$234.6896	$234.69	$234.70	$234.70
7 purchase totals =	$1,036.41		$1,123.0392	$1,123.03	$1,123.00	$1,123.20