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	$38.69	5.217%	$40.7085	$40.71	$40.70	$40.70
Purchase #2	$137.33	3.771%	$142.5087	$142.51	$142.50	$142.50
Purchase #3	$40.49	11.331%	$45.0779	$45.08	$45.10	$45.10
Purchase #4	$156.37	7.192%	$167.6161	$167.62	$167.60	$167.60
Purchase #5	$16.34	13.668%	$18.5734	$18.57	$18.55	$18.60
Purchase #6	$176.44	9.656%	$193.477	$193.48	$193.50	$193.50
Purchase #7	$34.81	7.506%	$37.4228	$37.42	$37.40	$37.40
7 purchase totals =	$600.47		$645.3844	$645.39	$645.35	$645.40