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	$32.72	4.233%	$34.105	$34.11	$34.10	$34.10
Purchase #2	$112.45	13.864%	$128.0401	$128.04	$128.05	$128.00
Purchase #3	$93.91	10.304%	$103.5865	$103.59	$103.60	$103.60
Purchase #4	$204.60	9.213%	$223.4498	$223.45	$223.45	$223.40
Purchase #5	$218.68	5.821%	$231.4094	$231.41	$231.40	$231.40
Purchase #6	$26.41	9.315%	$28.8701	$28.87	$28.85	$28.90
Purchase #7	$182.50	5.658%	$192.8259	$192.83	$192.85	$192.80
7 purchase totals =	$871.27		$942.2868	$942.30	$942.30	$942.20