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	$68.32	3.260%	$70.5472	$70.55	$70.55	$70.50
Purchase #2	$196.79	10.475%	$217.4038	$217.40	$217.40	$217.40
Purchase #3	$71.52	9.499%	$78.3137	$78.31	$78.30	$78.30
Purchase #4	$151.88	4.345%	$158.4792	$158.48	$158.50	$158.50
Purchase #5	$202.64	12.142%	$227.2445	$227.24	$227.25	$227.20
Purchase #6	$198.39	10.106%	$218.4393	$218.44	$218.45	$218.40
Purchase #7	$235.67	6.433%	$250.8307	$250.83	$250.85	$250.80
7 purchase totals =	$1,125.21		$1,221.2584	$1,221.25	$1,221.30	$1,221.10