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	$9.47	9.625%	$10.3815	$10.38	$10.40	$10.40
Purchase #2	$110.95	7.343%	$119.0971	$119.10	$119.10	$119.10
Purchase #3	$65.70	11.428%	$73.2082	$73.21	$73.20	$73.20
Purchase #4	$91.93	6.754%	$98.139	$98.14	$98.15	$98.10
Purchase #5	$51.75	4.172%	$53.909	$53.91	$53.90	$53.90
Purchase #6	$84.34	6.460%	$89.7884	$89.79	$89.80	$89.80
Purchase #7	$173.28	13.399%	$196.4978	$196.50	$196.50	$196.50
7 purchase totals =	$587.42		$641.0210	$641.03	$641.05	$641.00