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	$35.95	10.119%	$39.5878	$39.59	$39.60	$39.60
Purchase #2	$69.36	13.772%	$78.9123	$78.91	$78.90	$78.90
Purchase #3	$15.41	12.786%	$17.3803	$17.38	$17.40	$17.40
Purchase #4	$204.65	8.552%	$222.1517	$222.15	$222.15	$222.20
Purchase #5	$171.79	5.482%	$181.2075	$181.21	$181.20	$181.20
Purchase #6	$59.68	8.511%	$64.7594	$64.76	$64.75	$64.80
Purchase #7	$40.26	5.816%	$42.6015	$42.60	$42.60	$42.60
7 purchase totals =	$597.10		$646.6005	$646.60	$646.60	$646.70