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	$57.99	12.441%	$65.2045	$65.20	$65.20	$65.20
Purchase #2	$37.73	4.364%	$39.3765	$39.38	$39.40	$39.40
Purchase #3	$184.80	11.164%	$205.4311	$205.43	$205.45	$205.40
Purchase #4	$245.38	4.752%	$257.0405	$257.04	$257.05	$257.00
Purchase #5	$67.49	6.760%	$72.0523	$72.05	$72.05	$72.10
Purchase #6	$118.89	10.465%	$131.3318	$131.33	$131.35	$131.30
Purchase #7	$90.25	11.394%	$100.5331	$100.53	$100.55	$100.50
7 purchase totals =	$802.53		$870.9698	$870.96	$871.05	$870.90