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	$89.60	11.120%	$99.5635	$99.56	$99.55	$99.60
Purchase #2	$190.70	9.267%	$208.3722	$208.37	$208.35	$208.40
Purchase #3	$227.58	12.328%	$255.6361	$255.64	$255.65	$255.60
Purchase #4	$243.30	10.354%	$268.4913	$268.49	$268.50	$268.50
Purchase #5	$72.88	9.815%	$80.0332	$80.03	$80.05	$80.00
Purchase #6	$148.28	13.805%	$168.7501	$168.75	$168.75	$168.80
Purchase #7	$150.29	5.538%	$158.6131	$158.61	$158.60	$158.60
7 purchase totals =	$1,122.63		$1,239.4595	$1,239.45	$1,239.45	$1,239.50