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	$9.78	8.165%	$10.5785	$10.58	$10.60	$10.60
Purchase #2	$235.45	6.405%	$250.5306	$250.53	$250.55	$250.50
Purchase #3	$12.73	13.629%	$14.465	$14.47	$14.45	$14.50
Purchase #4	$201.48	10.837%	$223.3144	$223.31	$223.30	$223.30
Purchase #5	$56.32	9.398%	$61.613	$61.61	$61.60	$61.60
Purchase #6	$37.71	6.700%	$40.2366	$40.24	$40.25	$40.20
Purchase #7	$26.43	7.715%	$28.4691	$28.47	$28.45	$28.50
7 purchase totals =	$579.90		$629.2072	$629.21	$629.20	$629.20