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	$217.34	3.279%	$224.4666	$224.47	$224.45	$224.50
Purchase #2	$179.88	9.197%	$196.4236	$196.42	$196.40	$196.40
Purchase #3	$59.28	8.382%	$64.2488	$64.25	$64.25	$64.20
Purchase #4	$123.31	4.274%	$128.5803	$128.58	$128.60	$128.60
Purchase #5	$30.47	8.151%	$32.9536	$32.95	$32.95	$33.00
Purchase #6	$6.57	13.301%	$7.4439	$7.44	$7.45	$7.40
Purchase #7	$207.43	10.629%	$229.4777	$229.48	$229.50	$229.50
7 purchase totals =	$824.28		$883.5945	$883.59	$883.60	$883.60