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	$155.45	6.717%	$165.8916	$165.89	$165.90	$165.90
Purchase #2	$59.29	13.677%	$67.3991	$67.40	$67.40	$67.40
Purchase #3	$185.76	7.401%	$199.5081	$199.51	$199.50	$199.50
Purchase #4	$171.96	7.580%	$184.9946	$184.99	$185.00	$185.00
Purchase #5	$233.33	3.256%	$240.9272	$240.93	$240.95	$240.90
Purchase #6	$192.90	9.158%	$210.5658	$210.57	$210.55	$210.60
Purchase #7	$5.65	4.211%	$5.8879	$5.89	$5.90	$5.90
7 purchase totals =	$1,004.34		$1,075.1743	$1,075.18	$1,075.20	$1,075.20