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	$124.52	12.336%	$139.8808	$139.88	$139.90	$139.90
Purchase #2	$70.78	8.202%	$76.5854	$76.59	$76.60	$76.60
Purchase #3	$39.98	13.801%	$45.4976	$45.50	$45.50	$45.50
Purchase #4	$233.82	5.185%	$245.9436	$245.94	$245.95	$245.90
Purchase #5	$137.71	8.216%	$149.0243	$149.02	$149.00	$149.00
Purchase #6	$171.59	9.322%	$187.5856	$187.59	$187.60	$187.60
Purchase #7	$137.28	9.401%	$150.1857	$150.19	$150.20	$150.20
7 purchase totals =	$915.68		$994.7030	$994.71	$994.75	$994.70