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	$54.88	10.284%	$60.5239	$60.52	$60.50	$60.50
Purchase #2	$31.52	7.626%	$33.9237	$33.92	$33.90	$33.90
Purchase #3	$196.70	4.393%	$205.341	$205.34	$205.35	$205.30
Purchase #4	$213.56	7.630%	$229.8546	$229.85	$229.85	$229.90
Purchase #5	$19.43	8.800%	$21.1398	$21.14	$21.15	$21.10
Purchase #6	$206.35	8.507%	$223.9042	$223.90	$223.90	$223.90
Purchase #7	$60.59	6.616%	$64.5986	$64.60	$64.60	$64.60
7 purchase totals =	$783.03		$839.2858	$839.27	$839.25	$839.20