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	$36.71	11.323%	$40.8667	$40.87	$40.85	$40.90
Purchase #2	$194.55	8.643%	$211.365	$211.37	$211.35	$211.40
Purchase #3	$101.99	9.237%	$111.4108	$111.41	$111.40	$111.40
Purchase #4	$139.54	13.697%	$158.6528	$158.65	$158.65	$158.70
Purchase #5	$238.37	13.336%	$270.159	$270.16	$270.15	$270.20
Purchase #6	$171.99	13.319%	$194.8973	$194.90	$194.90	$194.90
Purchase #7	$147.68	3.270%	$152.5091	$152.51	$152.50	$152.50
7 purchase totals =	$1,030.83		$1,139.8607	$1,139.87	$1,139.80	$1,140.00