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	$230.80	11.732%	$257.8775	$257.88	$257.90	$257.90
Purchase #2	$191.44	11.269%	$213.0134	$213.01	$213.00	$213.00
Purchase #3	$69.69	13.277%	$78.9427	$78.94	$78.95	$78.90
Purchase #4	$88.33	9.304%	$96.5482	$96.55	$96.55	$96.50
Purchase #5	$121.84	6.853%	$130.1897	$130.19	$130.20	$130.20
Purchase #6	$131.74	10.302%	$145.3119	$145.31	$145.30	$145.30
Purchase #7	$61.63	9.447%	$67.4522	$67.45	$67.45	$67.50
7 purchase totals =	$895.47		$989.3356	$989.33	$989.35	$989.30