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	$100.90	11.588%	$112.5923	$112.59	$112.60	$112.60
Purchase #2	$186.43	12.765%	$210.2278	$210.23	$210.25	$210.20
Purchase #3	$87.82	7.288%	$94.2203	$94.22	$94.20	$94.20
Purchase #4	$83.75	13.538%	$95.0881	$95.09	$95.10	$95.10
Purchase #5	$37.25	11.838%	$41.6597	$41.66	$41.65	$41.70
Purchase #6	$80.76	6.516%	$86.0223	$86.02	$86.00	$86.00
Purchase #7	$89.61	10.407%	$98.9357	$98.94	$98.95	$98.90
7 purchase totals =	$666.52		$738.7462	$738.75	$738.75	$738.70