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	$248.66	5.334%	$261.9235	$261.92	$261.90	$261.90
Purchase #2	$106.58	10.315%	$117.5737	$117.57	$117.55	$117.60
Purchase #3	$142.42	12.182%	$159.7696	$159.77	$159.75	$159.80
Purchase #4	$33.89	13.251%	$38.3808	$38.38	$38.40	$38.40
Purchase #5	$105.58	11.300%	$117.5105	$117.51	$117.50	$117.50
Purchase #6	$168.42	10.148%	$185.5113	$185.51	$185.50	$185.50
Purchase #7	$200.35	7.535%	$215.4464	$215.45	$215.45	$215.40
7 purchase totals =	$1,005.90		$1,096.1158	$1,096.11	$1,096.05	$1,096.10