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	$19.34	10.171%	$21.3071	$21.31	$21.30	$21.30
Purchase #2	$27.83	7.234%	$29.8432	$29.84	$29.85	$29.80
Purchase #3	$159.98	7.171%	$171.4522	$171.45	$171.45	$171.50
Purchase #4	$101.42	10.372%	$111.9393	$111.94	$111.95	$111.90
Purchase #5	$53.96	12.246%	$60.5679	$60.57	$60.55	$60.60
Purchase #6	$10.38	4.825%	$10.8808	$10.88	$10.90	$10.90
Purchase #7	$92.66	5.787%	$98.0222	$98.02	$98.00	$98.00
7 purchase totals =	$465.57		$504.0127	$504.01	$504.00	$504.00