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	$129.33	7.794%	$139.41	$139.41	$139.40	$139.40
Purchase #2	$179.47	8.136%	$194.0717	$194.07	$194.05	$194.10
Purchase #3	$212.61	5.188%	$223.6402	$223.64	$223.65	$223.60
Purchase #4	$242.59	12.644%	$273.2631	$273.26	$273.25	$273.30
Purchase #5	$65.91	9.103%	$71.9098	$71.91	$71.90	$71.90
Purchase #6	$13.32	8.344%	$14.4314	$14.43	$14.45	$14.40
Purchase #7	$72.68	10.218%	$80.1064	$80.11	$80.10	$80.10
7 purchase totals =	$915.91		$996.8326	$996.83	$996.80	$996.80