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	$29.77	5.538%	$31.4187	$31.42	$31.40	$31.40
Purchase #2	$238.72	3.111%	$246.1466	$246.15	$246.15	$246.10
Purchase #3	$225.85	12.188%	$253.3766	$253.38	$253.40	$253.40
Purchase #4	$152.49	11.221%	$169.6009	$169.60	$169.60	$169.60
Purchase #5	$66.52	5.374%	$70.0948	$70.09	$70.10	$70.10
Purchase #6	$85.49	4.580%	$89.4054	$89.41	$89.40	$89.40
Purchase #7	$28.35	7.261%	$30.4085	$30.41	$30.40	$30.40
7 purchase totals =	$827.19		$890.4515	$890.46	$890.45	$890.40