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	$86.45	4.377%	$90.2339	$90.23	$90.25	$90.20
Purchase #2	$74.40	9.138%	$81.1987	$81.20	$81.20	$81.20
Purchase #3	$160.64	7.579%	$172.8149	$172.81	$172.80	$172.80
Purchase #4	$152.66	12.552%	$171.8219	$171.82	$171.80	$171.80
Purchase #5	$150.78	8.849%	$164.1225	$164.12	$164.10	$164.10
Purchase #6	$244.64	9.579%	$268.0741	$268.07	$268.05	$268.10
Purchase #7	$6.96	3.218%	$7.184	$7.18	$7.20	$7.20
7 purchase totals =	$876.53		$955.4500	$955.43	$955.40	$955.40