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	$67.46	5.503%	$71.1723	$71.17	$71.15	$71.20
Purchase #2	$137.60	13.546%	$156.2393	$156.24	$156.25	$156.20
Purchase #3	$56.94	9.736%	$62.4837	$62.48	$62.50	$62.50
Purchase #4	$65.96	10.471%	$72.8667	$72.87	$72.85	$72.90
Purchase #5	$11.28	5.131%	$11.8588	$11.86	$11.85	$11.90
Purchase #6	$44.90	3.394%	$46.4239	$46.42	$46.40	$46.40
Purchase #7	$204.93	10.667%	$226.7899	$226.79	$226.80	$226.80
7 purchase totals =	$589.07		$647.8346	$647.83	$647.80	$647.90