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	$43.71	13.432%	$49.5811	$49.58	$49.60	$49.60
Purchase #2	$180.41	9.148%	$196.9139	$196.91	$196.90	$196.90
Purchase #3	$140.37	7.318%	$150.6423	$150.64	$150.65	$150.60
Purchase #4	$89.88	6.724%	$95.9235	$95.92	$95.90	$95.90
Purchase #5	$20.59	8.853%	$22.4128	$22.41	$22.40	$22.40
Purchase #6	$31.83	12.629%	$35.8498	$35.85	$35.85	$35.80
Purchase #7	$241.52	7.258%	$259.0495	$259.05	$259.05	$259.00
7 purchase totals =	$748.31		$810.3729	$810.36	$810.35	$810.20