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	$53.33	11.307%	$59.36	$59.36	$59.35	$59.40
Purchase #2	$173.42	6.393%	$184.5067	$184.51	$184.50	$184.50
Purchase #3	$167.80	12.820%	$189.312	$189.31	$189.30	$189.30
Purchase #4	$146.88	7.823%	$158.3704	$158.37	$158.35	$158.40
Purchase #5	$122.42	7.742%	$131.8978	$131.90	$131.90	$131.90
Purchase #6	$52.96	7.699%	$57.0374	$57.04	$57.05	$57.00
Purchase #7	$38.54	6.598%	$41.0829	$41.08	$41.10	$41.10
7 purchase totals =	$755.35		$821.5672	$821.57	$821.55	$821.60