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	$35.75	8.867%	$38.92	$38.92	$38.90	$38.90
Purchase #2	$112.31	6.298%	$119.3833	$119.38	$119.40	$119.40
Purchase #3	$99.67	11.770%	$111.4012	$111.40	$111.40	$111.40
Purchase #4	$195.72	9.816%	$214.9319	$214.93	$214.95	$214.90
Purchase #5	$62.76	13.660%	$71.333	$71.33	$71.35	$71.30
Purchase #6	$199.27	10.574%	$220.3408	$220.34	$220.35	$220.30
Purchase #7	$202.48	5.275%	$213.1608	$213.16	$213.15	$213.20
7 purchase totals =	$907.96		$989.4710	$989.46	$989.50	$989.40