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	$38.88	11.856%	$43.4896	$43.49	$43.50	$43.50
Purchase #2	$237.30	5.500%	$250.3515	$250.35	$250.35	$250.40
Purchase #3	$29.64	4.400%	$30.9442	$30.94	$30.95	$30.90
Purchase #4	$148.56	11.211%	$165.2151	$165.22	$165.20	$165.20
Purchase #5	$104.82	6.807%	$111.9551	$111.96	$111.95	$112.00
Purchase #6	$243.34	5.566%	$256.8843	$256.88	$256.90	$256.90
Purchase #7	$186.92	6.811%	$199.6511	$199.65	$199.65	$199.70
7 purchase totals =	$989.46		$1,058.4909	$1,058.49	$1,058.50	$1,058.60