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	$40.85	7.152%	$43.7716	$43.77	$43.75	$43.80
Purchase #2	$114.46	12.229%	$128.4573	$128.46	$128.45	$128.50
Purchase #3	$46.88	13.663%	$53.2852	$53.29	$53.30	$53.30
Purchase #4	$65.43	13.743%	$74.422	$74.42	$74.40	$74.40
Purchase #5	$41.96	11.567%	$46.8135	$46.81	$46.80	$46.80
Purchase #6	$204.39	13.116%	$231.1978	$231.20	$231.20	$231.20
Purchase #7	$55.90	7.253%	$59.9544	$59.95	$59.95	$60.00
7 purchase totals =	$569.87		$637.9018	$637.90	$637.85	$638.00