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	$41.62	4.230%	$43.3805	$43.38	$43.40	$43.40
Purchase #2	$91.69	10.401%	$101.2267	$101.23	$101.25	$101.20
Purchase #3	$237.55	6.541%	$253.0881	$253.09	$253.10	$253.10
Purchase #4	$156.61	12.306%	$175.8824	$175.88	$175.90	$175.90
Purchase #5	$12.32	9.336%	$13.4702	$13.47	$13.45	$13.50
Purchase #6	$103.38	9.185%	$112.8755	$112.88	$112.90	$112.90
Purchase #7	$194.34	10.787%	$215.3035	$215.30	$215.30	$215.30
7 purchase totals =	$837.51		$915.2269	$915.23	$915.30	$915.30