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	$139.66	11.313%	$155.4597	$155.46	$155.45	$155.50
Purchase #2	$31.48	7.274%	$33.7699	$33.77	$33.75	$33.80
Purchase #3	$165.59	4.825%	$173.5797	$173.58	$173.60	$173.60
Purchase #4	$36.25	12.369%	$40.7338	$40.73	$40.75	$40.70
Purchase #5	$196.93	12.709%	$221.9578	$221.96	$221.95	$222.00
Purchase #6	$48.86	13.358%	$55.3867	$55.39	$55.40	$55.40
Purchase #7	$112.35	13.480%	$127.4948	$127.49	$127.50	$127.50
7 purchase totals =	$731.12		$808.3824	$808.38	$808.40	$808.50