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	$116.58	12.584%	$131.2504	$131.25	$131.25	$131.30
Purchase #2	$67.46	6.546%	$71.8759	$71.88	$71.90	$71.90
Purchase #3	$215.75	9.488%	$236.2204	$236.22	$236.20	$236.20
Purchase #4	$113.28	7.335%	$121.5891	$121.59	$121.60	$121.60
Purchase #5	$86.45	5.308%	$91.0388	$91.04	$91.05	$91.00
Purchase #6	$59.94	7.314%	$64.324	$64.32	$64.30	$64.30
Purchase #7	$156.59	12.488%	$176.145	$176.15	$176.15	$176.10
7 purchase totals =	$816.05		$892.4436	$892.45	$892.45	$892.40