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	$25.88	5.570%	$27.3215	$27.32	$27.30	$27.30
Purchase #2	$154.34	4.110%	$160.6834	$160.68	$160.70	$160.70
Purchase #3	$205.59	5.675%	$217.2572	$217.26	$217.25	$217.30
Purchase #4	$128.38	10.427%	$141.7662	$141.77	$141.75	$141.80
Purchase #5	$250.52	8.328%	$271.3833	$271.38	$271.40	$271.40
Purchase #6	$106.53	11.707%	$119.0015	$119.00	$119.00	$119.00
Purchase #7	$73.76	9.667%	$80.8904	$80.89	$80.90	$80.90
7 purchase totals =	$945.00		$1,018.3035	$1,018.30	$1,018.30	$1,018.40