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	$82.43	12.173%	$92.4642	$92.46	$92.45	$92.50
Purchase #2	$143.61	6.810%	$153.3898	$153.39	$153.40	$153.40
Purchase #3	$108.66	4.172%	$113.1933	$113.19	$113.20	$113.20
Purchase #4	$155.72	10.230%	$171.6502	$171.65	$171.65	$171.70
Purchase #5	$245.51	10.183%	$270.5103	$270.51	$270.50	$270.50
Purchase #6	$166.71	8.369%	$180.662	$180.66	$180.65	$180.70
Purchase #7	$58.58	13.681%	$66.5943	$66.59	$66.60	$66.60
7 purchase totals =	$961.22		$1,048.4641	$1,048.45	$1,048.45	$1,048.60