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	$105.61	13.416%	$119.7786	$119.78	$119.80	$119.80
Purchase #2	$60.37	13.860%	$68.7373	$68.74	$68.75	$68.70
Purchase #3	$71.32	12.197%	$80.0189	$80.02	$80.00	$80.00
Purchase #4	$84.37	7.238%	$90.4767	$90.48	$90.50	$90.50
Purchase #5	$84.89	12.315%	$95.3442	$95.34	$95.35	$95.30
Purchase #6	$19.25	6.703%	$20.5403	$20.54	$20.55	$20.50
Purchase #7	$111.40	6.681%	$118.8426	$118.84	$118.85	$118.80
7 purchase totals =	$537.21		$593.7386	$593.74	$593.80	$593.60