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	$56.77	10.800%	$62.9012	$62.90	$62.90	$62.90
Purchase #2	$206.25	4.437%	$215.4013	$215.40	$215.40	$215.40
Purchase #3	$150.32	9.426%	$164.4892	$164.49	$164.50	$164.50
Purchase #4	$138.56	9.805%	$152.1458	$152.15	$152.15	$152.10
Purchase #5	$152.49	10.635%	$168.7073	$168.71	$168.70	$168.70
Purchase #6	$224.29	7.161%	$240.3514	$240.35	$240.35	$240.40
Purchase #7	$237.72	10.730%	$263.2274	$263.23	$263.25	$263.20
7 purchase totals =	$1,166.40		$1,267.2236	$1,267.23	$1,267.25	$1,267.20