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	$36.76	4.802%	$38.5252	$38.53	$38.55	$38.50
Purchase #2	$190.52	11.400%	$212.2393	$212.24	$212.25	$212.20
Purchase #3	$140.84	5.352%	$148.3778	$148.38	$148.40	$148.40
Purchase #4	$46.36	3.698%	$48.0744	$48.07	$48.05	$48.10
Purchase #5	$196.72	13.205%	$222.6969	$222.70	$222.70	$222.70
Purchase #6	$163.90	11.805%	$183.2484	$183.25	$183.25	$183.20
Purchase #7	$176.27	11.449%	$196.4512	$196.45	$196.45	$196.50
7 purchase totals =	$951.37		$1,049.6132	$1,049.62	$1,049.65	$1,049.60