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	$64.26	12.268%	$72.1434	$72.14	$72.15	$72.10
Purchase #2	$49.48	10.128%	$54.4913	$54.49	$54.50	$54.50
Purchase #3	$83.77	11.678%	$93.5527	$93.55	$93.55	$93.60
Purchase #4	$68.81	13.510%	$78.1062	$78.11	$78.10	$78.10
Purchase #5	$78.44	5.419%	$82.6907	$82.69	$82.70	$82.70
Purchase #6	$218.84	8.466%	$237.367	$237.37	$237.35	$237.40
Purchase #7	$189.67	7.206%	$203.3376	$203.34	$203.35	$203.30
7 purchase totals =	$753.27		$821.6889	$821.69	$821.70	$821.70