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	$173.46	3.698%	$179.8746	$179.87	$179.85	$179.90
Purchase #2	$78.39	4.476%	$81.8987	$81.90	$81.90	$81.90
Purchase #3	$213.39	7.573%	$229.55	$229.55	$229.55	$229.60
Purchase #4	$81.61	11.375%	$90.8931	$90.89	$90.90	$90.90
Purchase #5	$12.45	12.534%	$14.0105	$14.01	$14.00	$14.00
Purchase #6	$183.36	12.665%	$206.5825	$206.58	$206.60	$206.60
Purchase #7	$33.44	11.843%	$37.4003	$37.40	$37.40	$37.40
7 purchase totals =	$776.10		$840.2097	$840.20	$840.20	$840.30