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	$232.33	10.394%	$256.4784	$256.48	$256.50	$256.50
Purchase #2	$57.47	5.204%	$60.4607	$60.46	$60.45	$60.50
Purchase #3	$193.57	11.129%	$215.1124	$215.11	$215.10	$215.10
Purchase #4	$123.99	3.185%	$127.9391	$127.94	$127.95	$127.90
Purchase #5	$44.95	13.505%	$51.0205	$51.02	$51.00	$51.00
Purchase #6	$101.89	4.503%	$106.4781	$106.48	$106.50	$106.50
Purchase #7	$211.43	4.781%	$221.5385	$221.54	$221.55	$221.50
7 purchase totals =	$965.63		$1,039.0277	$1,039.03	$1,039.05	$1,039.00