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	$51.92	3.787%	$53.8862	$53.89	$53.90	$53.90
Purchase #2	$99.35	13.547%	$112.8089	$112.81	$112.80	$112.80
Purchase #3	$50.35	4.652%	$52.6923	$52.69	$52.70	$52.70
Purchase #4	$81.97	5.400%	$86.3964	$86.40	$86.40	$86.40
Purchase #5	$61.29	9.802%	$67.2976	$67.30	$67.30	$67.30
Purchase #6	$131.57	8.186%	$142.3403	$142.34	$142.35	$142.30
Purchase #7	$81.50	9.428%	$89.1838	$89.18	$89.20	$89.20
7 purchase totals =	$557.95		$604.6055	$604.61	$604.65	$604.60