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	$29.44	10.338%	$32.4835	$32.48	$32.50	$32.50
Purchase #2	$21.35	4.698%	$22.353	$22.35	$22.35	$22.40
Purchase #3	$164.81	4.231%	$171.7831	$171.78	$171.80	$171.80
Purchase #4	$171.86	4.633%	$179.8223	$179.82	$179.80	$179.80
Purchase #5	$84.98	6.809%	$90.7663	$90.77	$90.75	$90.80
Purchase #6	$43.26	3.489%	$44.7693	$44.77	$44.75	$44.80
Purchase #7	$24.47	12.238%	$27.4646	$27.46	$27.45	$27.50
7 purchase totals =	$540.17		$569.4421	$569.43	$569.40	$569.60