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	$187.84	6.785%	$200.5849	$200.58	$200.60	$200.60
Purchase #2	$25.92	13.468%	$29.4109	$29.41	$29.40	$29.40
Purchase #3	$34.65	13.412%	$39.2973	$39.30	$39.30	$39.30
Purchase #4	$158.43	10.185%	$174.5661	$174.57	$174.55	$174.60
Purchase #5	$190.89	13.387%	$216.4444	$216.44	$216.45	$216.40
Purchase #6	$64.76	12.461%	$72.8297	$72.83	$72.85	$72.80
Purchase #7	$61.39	6.294%	$65.2539	$65.25	$65.25	$65.30
7 purchase totals =	$723.88		$798.3872	$798.38	$798.40	$798.40