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	$203.89	8.215%	$220.6396	$220.64	$220.65	$220.60
Purchase #2	$142.34	5.754%	$150.5302	$150.53	$150.55	$150.50
Purchase #3	$123.61	6.225%	$131.3047	$131.30	$131.30	$131.30
Purchase #4	$45.30	4.470%	$47.3249	$47.32	$47.30	$47.30
Purchase #5	$225.80	10.506%	$249.5225	$249.52	$249.50	$249.50
Purchase #6	$191.94	9.200%	$209.5985	$209.60	$209.60	$209.60
Purchase #7	$236.28	4.519%	$246.9575	$246.96	$246.95	$247.00
7 purchase totals =	$1,169.16		$1,255.8779	$1,255.87	$1,255.85	$1,255.80