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	$37.49	8.389%	$40.635	$40.64	$40.65	$40.60
Purchase #2	$35.64	6.386%	$37.916	$37.92	$37.90	$37.90
Purchase #3	$86.52	4.477%	$90.3935	$90.39	$90.40	$90.40
Purchase #4	$71.36	12.328%	$80.1573	$80.16	$80.15	$80.20
Purchase #5	$9.70	7.164%	$10.3949	$10.39	$10.40	$10.40
Purchase #6	$187.41	11.715%	$209.3651	$209.37	$209.35	$209.40
Purchase #7	$16.28	10.434%	$17.9787	$17.98	$18.00	$18.00
7 purchase totals =	$444.40		$486.8405	$486.85	$486.85	$486.90