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	$240.37	12.535%	$270.5004	$270.50	$270.50	$270.50
Purchase #2	$172.74	12.169%	$193.7607	$193.76	$193.75	$193.80
Purchase #3	$55.61	10.438%	$61.4146	$61.41	$61.40	$61.40
Purchase #4	$28.49	11.857%	$31.8681	$31.87	$31.85	$31.90
Purchase #5	$202.47	9.767%	$222.2452	$222.25	$222.25	$222.20
Purchase #6	$136.37	11.775%	$152.4276	$152.43	$152.45	$152.40
Purchase #7	$184.32	8.536%	$200.0536	$200.05	$200.05	$200.10
7 purchase totals =	$1,020.37		$1,132.2702	$1,132.27	$1,132.25	$1,132.30