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	$6.48	9.849%	$7.1182	$7.12	$7.10	$7.10
Purchase #2	$199.95	13.264%	$226.4714	$226.47	$226.45	$226.50
Purchase #3	$242.79	5.270%	$255.585	$255.59	$255.60	$255.60
Purchase #4	$116.39	3.356%	$120.296	$120.30	$120.30	$120.30
Purchase #5	$13.89	7.283%	$14.9016	$14.90	$14.90	$14.90
Purchase #6	$211.73	13.412%	$240.1272	$240.13	$240.15	$240.10
Purchase #7	$19.50	5.772%	$20.6255	$20.63	$20.65	$20.60
7 purchase totals =	$810.73		$885.1249	$885.14	$885.15	$885.10