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	$8.47	4.740%	$8.8715	$8.87	$8.85	$8.90
Purchase #2	$208.80	7.564%	$224.5936	$224.59	$224.60	$224.60
Purchase #3	$72.33	10.729%	$80.0903	$80.09	$80.10	$80.10
Purchase #4	$66.46	8.370%	$72.0227	$72.02	$72.00	$72.00
Purchase #5	$61.52	9.515%	$67.3736	$67.37	$67.35	$67.40
Purchase #6	$28.87	9.715%	$31.6747	$31.67	$31.65	$31.70
Purchase #7	$142.85	6.452%	$152.0667	$152.07	$152.05	$152.10
7 purchase totals =	$589.30		$636.6931	$636.68	$636.60	$636.80