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	$21.66	11.549%	$24.1615	$24.16	$24.15	$24.20
Purchase #2	$46.34	5.545%	$48.9096	$48.91	$48.90	$48.90
Purchase #3	$83.84	3.607%	$86.8641	$86.86	$86.85	$86.90
Purchase #4	$74.90	5.272%	$78.8487	$78.85	$78.85	$78.80
Purchase #5	$126.76	5.325%	$133.51	$133.51	$133.50	$133.50
Purchase #6	$172.32	7.145%	$184.6323	$184.63	$184.65	$184.60
Purchase #7	$134.29	13.548%	$152.4836	$152.48	$152.50	$152.50
7 purchase totals =	$660.11		$709.4098	$709.40	$709.40	$709.40