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	$37.89	6.601%	$40.3911	$40.39	$40.40	$40.40
Purchase #2	$217.45	9.709%	$238.5622	$238.56	$238.55	$238.60
Purchase #3	$33.89	9.481%	$37.1031	$37.10	$37.10	$37.10
Purchase #4	$204.30	4.512%	$213.518	$213.52	$213.50	$213.50
Purchase #5	$105.46	10.568%	$116.605	$116.61	$116.60	$116.60
Purchase #6	$231.50	11.765%	$258.736	$258.74	$258.75	$258.70
Purchase #7	$176.29	11.539%	$196.6321	$196.63	$196.65	$196.60
7 purchase totals =	$1,006.78		$1,101.5475	$1,101.55	$1,101.55	$1,101.50