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	$38.74	4.748%	$40.5794	$40.58	$40.60	$40.60
Purchase #2	$28.65	10.439%	$31.6408	$31.64	$31.65	$31.60
Purchase #3	$18.81	11.668%	$21.0048	$21.00	$21.00	$21.00
Purchase #4	$198.48	7.547%	$213.4593	$213.46	$213.45	$213.50
Purchase #5	$152.89	9.854%	$167.9558	$167.96	$167.95	$168.00
Purchase #6	$217.48	11.831%	$243.2101	$243.21	$243.20	$243.20
Purchase #7	$38.47	7.752%	$41.4522	$41.45	$41.45	$41.50
7 purchase totals =	$693.52		$759.3024	$759.30	$759.30	$759.40