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	$51.79	5.268%	$54.5183	$54.52	$54.50	$54.50
Purchase #2	$30.50	12.849%	$34.4189	$34.42	$34.40	$34.40
Purchase #3	$167.51	13.726%	$190.5024	$190.50	$190.50	$190.50
Purchase #4	$164.67	13.753%	$187.3171	$187.32	$187.30	$187.30
Purchase #5	$71.32	7.228%	$76.475	$76.48	$76.50	$76.50
Purchase #6	$79.85	4.296%	$83.2804	$83.28	$83.30	$83.30
Purchase #7	$30.56	13.482%	$34.6801	$34.68	$34.70	$34.70
7 purchase totals =	$596.20		$661.1922	$661.20	$661.20	$661.20