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	$71.68	12.277%	$80.4802	$80.48	$80.50	$80.50
Purchase #2	$110.72	7.814%	$119.3717	$119.37	$119.35	$119.40
Purchase #3	$68.46	11.734%	$76.4931	$76.49	$76.50	$76.50
Purchase #4	$172.59	4.232%	$179.894	$179.89	$179.90	$179.90
Purchase #5	$192.41	5.353%	$202.7097	$202.71	$202.70	$202.70
Purchase #6	$163.45	12.663%	$184.1477	$184.15	$184.15	$184.10
Purchase #7	$183.91	6.800%	$196.4159	$196.42	$196.40	$196.40
7 purchase totals =	$963.22		$1,039.5123	$1,039.51	$1,039.50	$1,039.50