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	$10.78	10.576%	$11.9201	$11.92	$11.90	$11.90
Purchase #2	$110.89	11.750%	$123.9196	$123.92	$123.90	$123.90
Purchase #3	$95.69	13.774%	$108.8703	$108.87	$108.85	$108.90
Purchase #4	$22.35	10.436%	$24.6824	$24.68	$24.70	$24.70
Purchase #5	$27.30	3.299%	$28.2006	$28.20	$28.20	$28.20
Purchase #6	$110.39	6.782%	$117.8766	$117.88	$117.90	$117.90
Purchase #7	$78.41	10.762%	$86.8485	$86.85	$86.85	$86.80
7 purchase totals =	$455.81		$502.3181	$502.32	$502.30	$502.30