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	$11.62	6.552%	$12.3813	$12.38	$12.40	$12.40
Purchase #2	$53.35	6.120%	$56.615	$56.62	$56.60	$56.60
Purchase #3	$56.56	7.747%	$60.9417	$60.94	$60.95	$60.90
Purchase #4	$54.72	13.222%	$61.9551	$61.96	$61.95	$62.00
Purchase #5	$168.98	11.859%	$189.0193	$189.02	$189.00	$189.00
Purchase #6	$50.78	6.653%	$54.1584	$54.16	$54.15	$54.20
Purchase #7	$168.43	8.319%	$182.4417	$182.44	$182.45	$182.40
7 purchase totals =	$564.44		$617.5125	$617.52	$617.50	$617.50