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	$211.40	3.421%	$218.632	$218.63	$218.65	$218.60
Purchase #2	$98.47	7.213%	$105.5726	$105.57	$105.55	$105.60
Purchase #3	$117.88	4.783%	$123.5182	$123.52	$123.50	$123.50
Purchase #4	$176.44	7.692%	$190.0118	$190.01	$190.00	$190.00
Purchase #5	$117.47	3.450%	$121.5227	$121.52	$121.50	$121.50
Purchase #6	$167.64	8.840%	$182.4594	$182.46	$182.45	$182.50
Purchase #7	$58.25	6.611%	$62.1009	$62.10	$62.10	$62.10
7 purchase totals =	$947.55		$1,003.8176	$1,003.81	$1,003.75	$1,003.80