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	$53.64	4.668%	$56.1439	$56.14	$56.15	$56.10
Purchase #2	$148.78	4.814%	$155.9423	$155.94	$155.95	$155.90
Purchase #3	$28.50	11.862%	$31.8807	$31.88	$31.90	$31.90
Purchase #4	$140.76	10.122%	$155.0077	$155.01	$155.00	$155.00
Purchase #5	$19.74	10.856%	$21.883	$21.88	$21.90	$21.90
Purchase #6	$233.89	7.408%	$251.2166	$251.22	$251.20	$251.20
Purchase #7	$208.89	9.106%	$227.9115	$227.91	$227.90	$227.90
7 purchase totals =	$834.20		$899.9857	$899.98	$900.00	$899.90