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	$78.30	7.298%	$84.0143	$84.01	$84.00	$84.00
Purchase #2	$109.57	13.405%	$124.2579	$124.26	$124.25	$124.30
Purchase #3	$59.64	6.413%	$63.4647	$63.46	$63.45	$63.50
Purchase #4	$194.42	12.863%	$219.4282	$219.43	$219.45	$219.40
Purchase #5	$33.37	11.772%	$37.2983	$37.30	$37.30	$37.30
Purchase #6	$48.67	5.467%	$51.3308	$51.33	$51.35	$51.30
Purchase #7	$106.90	4.228%	$111.4197	$111.42	$111.40	$111.40
7 purchase totals =	$630.87		$691.2139	$691.21	$691.20	$691.20