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	$89.92	9.819%	$98.7492	$98.75	$98.75	$98.70
Purchase #2	$95.53	13.362%	$108.2947	$108.29	$108.30	$108.30
Purchase #3	$46.43	9.783%	$50.9722	$50.97	$50.95	$51.00
Purchase #4	$69.52	4.120%	$72.3842	$72.38	$72.40	$72.40
Purchase #5	$82.98	8.464%	$90.0034	$90.00	$90.00	$90.00
Purchase #6	$56.55	8.134%	$61.1498	$61.15	$61.15	$61.10
Purchase #7	$41.50	10.695%	$45.9384	$45.94	$45.95	$45.90
7 purchase totals =	$482.43		$527.4919	$527.48	$527.50	$527.40