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	$36.40	10.223%	$40.1212	$40.12	$40.10	$40.10
Purchase #2	$165.89	3.720%	$172.0611	$172.06	$172.05	$172.10
Purchase #3	$17.89	3.298%	$18.48	$18.48	$18.50	$18.50
Purchase #4	$45.98	3.708%	$47.6849	$47.68	$47.70	$47.70
Purchase #5	$111.36	10.740%	$123.3201	$123.32	$123.30	$123.30
Purchase #6	$50.50	8.188%	$54.6349	$54.63	$54.65	$54.60
Purchase #7	$45.63	8.678%	$49.5898	$49.59	$49.60	$49.60
7 purchase totals =	$473.65		$505.8920	$505.88	$505.90	$505.90