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	$19.89	12.520%	$22.3802	$22.38	$22.40	$22.40
Purchase #2	$216.28	9.326%	$236.4503	$236.45	$236.45	$236.50
Purchase #3	$53.61	11.682%	$59.8727	$59.87	$59.85	$59.90
Purchase #4	$133.63	10.667%	$147.8843	$147.88	$147.90	$147.90
Purchase #5	$155.93	13.437%	$176.8823	$176.88	$176.90	$176.90
Purchase #6	$117.98	11.385%	$131.412	$131.41	$131.40	$131.40
Purchase #7	$202.50	7.253%	$217.1873	$217.19	$217.20	$217.20
7 purchase totals =	$899.82		$992.0691	$992.06	$992.10	$992.20