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	$105.29	6.646%	$112.2876	$112.29	$112.30	$112.30
Purchase #2	$103.91	7.214%	$111.4061	$111.41	$111.40	$111.40
Purchase #3	$169.89	11.239%	$188.9839	$188.98	$189.00	$189.00
Purchase #4	$13.64	5.354%	$14.3703	$14.37	$14.35	$14.40
Purchase #5	$137.68	6.254%	$146.2905	$146.29	$146.30	$146.30
Purchase #6	$35.64	11.814%	$39.8505	$39.85	$39.85	$39.90
Purchase #7	$136.40	8.138%	$147.5002	$147.50	$147.50	$147.50
7 purchase totals =	$702.45		$760.6891	$760.69	$760.70	$760.80