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	$29.69	10.530%	$32.8164	$32.82	$32.80	$32.80
Purchase #2	$41.73	12.342%	$46.8803	$46.88	$46.90	$46.90
Purchase #3	$227.43	13.824%	$258.8699	$258.87	$258.85	$258.90
Purchase #4	$175.96	3.557%	$182.2189	$182.22	$182.20	$182.20
Purchase #5	$147.72	11.646%	$164.9235	$164.92	$164.90	$164.90
Purchase #6	$97.52	11.644%	$108.8752	$108.88	$108.90	$108.90
Purchase #7	$201.62	4.176%	$210.0397	$210.04	$210.05	$210.00
7 purchase totals =	$921.67		$1,004.6239	$1,004.63	$1,004.60	$1,004.60