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	$24.94	9.767%	$27.3759	$27.38	$27.40	$27.40
Purchase #2	$36.49	8.229%	$39.4928	$39.49	$39.50	$39.50
Purchase #3	$201.36	8.604%	$218.685	$218.69	$218.70	$218.70
Purchase #4	$222.72	11.355%	$248.0099	$248.01	$248.00	$248.00
Purchase #5	$70.88	10.874%	$78.5875	$78.59	$78.60	$78.60
Purchase #6	$218.61	6.666%	$233.1825	$233.18	$233.20	$233.20
Purchase #7	$242.64	6.669%	$258.8217	$258.82	$258.80	$258.80
7 purchase totals =	$1,017.64		$1,104.1553	$1,104.16	$1,104.20	$1,104.20