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	$150.46	11.775%	$168.1767	$168.18	$168.20	$168.20
Purchase #2	$237.64	11.228%	$264.3222	$264.32	$264.30	$264.30
Purchase #3	$167.97	8.826%	$182.795	$182.80	$182.80	$182.80
Purchase #4	$27.53	4.209%	$28.6887	$28.69	$28.70	$28.70
Purchase #5	$162.89	8.328%	$176.4555	$176.46	$176.45	$176.50
Purchase #6	$19.25	5.147%	$20.2408	$20.24	$20.25	$20.20
Purchase #7	$80.40	12.613%	$90.5409	$90.54	$90.55	$90.50
7 purchase totals =	$846.14		$931.2198	$931.23	$931.25	$931.20