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	$49.90	8.862%	$54.3221	$54.32	$54.30	$54.30
Purchase #2	$162.49	11.360%	$180.9489	$180.95	$180.95	$180.90
Purchase #3	$170.60	10.745%	$188.931	$188.93	$188.95	$188.90
Purchase #4	$85.53	3.527%	$88.5466	$88.55	$88.55	$88.50
Purchase #5	$126.98	12.168%	$142.4309	$142.43	$142.45	$142.40
Purchase #6	$80.39	10.606%	$88.9162	$88.92	$88.90	$88.90
Purchase #7	$164.89	9.708%	$180.8975	$180.90	$180.90	$180.90
7 purchase totals =	$840.78		$924.9932	$925.00	$925.00	$924.80