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	$229.38	9.243%	$250.5816	$250.58	$250.60	$250.60
Purchase #2	$53.40	9.420%	$58.4303	$58.43	$58.45	$58.40
Purchase #3	$73.53	7.291%	$78.8911	$78.89	$78.90	$78.90
Purchase #4	$237.72	11.604%	$265.305	$265.31	$265.30	$265.30
Purchase #5	$163.28	11.650%	$182.3021	$182.30	$182.30	$182.30
Purchase #6	$87.96	4.612%	$92.0167	$92.02	$92.00	$92.00
Purchase #7	$41.96	4.689%	$43.9275	$43.93	$43.95	$43.90
7 purchase totals =	$887.23		$971.4543	$971.46	$971.50	$971.40