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	$90.41	11.102%	$100.4473	$100.45	$100.45	$100.40
Purchase #2	$59.32	3.673%	$61.4988	$61.50	$61.50	$61.50
Purchase #3	$169.92	10.431%	$187.6444	$187.64	$187.65	$187.60
Purchase #4	$98.60	11.324%	$109.7655	$109.77	$109.75	$109.80
Purchase #5	$174.88	4.540%	$182.8196	$182.82	$182.80	$182.80
Purchase #6	$165.90	4.243%	$172.9391	$172.94	$172.95	$172.90
Purchase #7	$12.26	9.410%	$13.4137	$13.41	$13.40	$13.40
7 purchase totals =	$771.29		$828.5284	$828.53	$828.50	$828.40