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	$140.92	10.589%	$155.842	$155.84	$155.85	$155.80
Purchase #2	$93.50	10.487%	$103.3053	$103.31	$103.30	$103.30
Purchase #3	$81.66	5.496%	$86.148	$86.15	$86.15	$86.10
Purchase #4	$59.41	7.689%	$63.978	$63.98	$64.00	$64.00
Purchase #5	$90.63	7.663%	$97.575	$97.58	$97.60	$97.60
Purchase #6	$85.72	4.766%	$89.8054	$89.81	$89.80	$89.80
Purchase #7	$205.64	6.480%	$218.9655	$218.97	$218.95	$219.00
7 purchase totals =	$757.48		$815.6192	$815.64	$815.65	$815.60