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	$49.64	12.815%	$56.0014	$56.00	$56.00	$56.00
Purchase #2	$248.69	5.485%	$262.3306	$262.33	$262.35	$262.30
Purchase #3	$152.38	12.461%	$171.3681	$171.37	$171.35	$171.40
Purchase #4	$242.35	13.850%	$275.9155	$275.92	$275.90	$275.90
Purchase #5	$140.96	10.763%	$156.1315	$156.13	$156.15	$156.10
Purchase #6	$78.88	8.213%	$85.3584	$85.36	$85.35	$85.40
Purchase #7	$95.55	3.276%	$98.6802	$98.68	$98.70	$98.70
7 purchase totals =	$1,008.45		$1,105.7857	$1,105.79	$1,105.80	$1,105.80