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	$50.53	10.515%	$55.8432	$55.84	$55.85	$55.80
Purchase #2	$95.85	5.483%	$101.1055	$101.11	$101.10	$101.10
Purchase #3	$12.46	4.504%	$13.0212	$13.02	$13.00	$13.00
Purchase #4	$47.85	12.519%	$53.8403	$53.84	$53.85	$53.80
Purchase #5	$118.94	10.834%	$131.826	$131.83	$131.85	$131.80
Purchase #6	$244.31	7.686%	$263.0877	$263.09	$263.10	$263.10
Purchase #7	$44.96	3.813%	$46.6743	$46.67	$46.65	$46.70
7 purchase totals =	$614.90		$665.3982	$665.40	$665.40	$665.30