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	$131.58	6.298%	$139.8669	$139.87	$139.85	$139.90
Purchase #2	$12.73	8.609%	$13.8259	$13.83	$13.85	$13.80
Purchase #3	$155.46	8.446%	$168.5902	$168.59	$168.60	$168.60
Purchase #4	$195.40	13.307%	$221.4019	$221.40	$221.40	$221.40
Purchase #5	$192.30	10.301%	$212.1088	$212.11	$212.10	$212.10
Purchase #6	$218.75	10.869%	$242.5259	$242.53	$242.55	$242.50
Purchase #7	$242.59	8.867%	$264.1005	$264.10	$264.10	$264.10
7 purchase totals =	$1,148.81		$1,262.4201	$1,262.43	$1,262.45	$1,262.40