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	$91.75	9.611%	$100.5681	$100.57	$100.55	$100.60
Purchase #2	$61.92	6.638%	$66.0302	$66.03	$66.05	$66.00
Purchase #3	$236.52	9.708%	$259.4814	$259.48	$259.50	$259.50
Purchase #4	$128.25	11.361%	$142.8205	$142.82	$142.80	$142.80
Purchase #5	$222.40	12.414%	$250.0087	$250.01	$250.00	$250.00
Purchase #6	$59.75	10.322%	$65.9174	$65.92	$65.90	$65.90
Purchase #7	$34.79	12.583%	$39.1676	$39.17	$39.15	$39.20
7 purchase totals =	$835.38		$923.9939	$924.00	$923.95	$924.00