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	$123.41	10.212%	$136.0126	$136.01	$136.00	$136.00
Purchase #2	$65.39	3.843%	$67.9029	$67.90	$67.90	$67.90
Purchase #3	$90.50	4.340%	$94.4277	$94.43	$94.45	$94.40
Purchase #4	$152.89	11.798%	$170.928	$170.93	$170.95	$170.90
Purchase #5	$201.46	9.874%	$221.3522	$221.35	$221.35	$221.40
Purchase #6	$107.87	8.321%	$116.8459	$116.85	$116.85	$116.80
Purchase #7	$41.35	3.722%	$42.889	$42.89	$42.90	$42.90
7 purchase totals =	$782.87		$850.3583	$850.36	$850.40	$850.30