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	$82.25	10.110%	$90.5655	$90.57	$90.55	$90.60
Purchase #2	$97.78	4.627%	$102.3043	$102.30	$102.30	$102.30
Purchase #3	$99.48	10.866%	$110.2895	$110.29	$110.30	$110.30
Purchase #4	$131.74	3.368%	$136.177	$136.18	$136.20	$136.20
Purchase #5	$28.33	10.616%	$31.3375	$31.34	$31.35	$31.30
Purchase #6	$97.97	10.745%	$108.4969	$108.50	$108.50	$108.50
Purchase #7	$200.64	3.803%	$208.2703	$208.27	$208.25	$208.30
7 purchase totals =	$738.19		$787.4410	$787.45	$787.45	$787.50