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	$225.83	10.267%	$249.016	$249.02	$249.00	$249.00
Purchase #2	$51.37	9.232%	$56.1125	$56.11	$56.10	$56.10
Purchase #3	$99.25	10.321%	$109.4936	$109.49	$109.50	$109.50
Purchase #4	$22.36	13.769%	$25.4387	$25.44	$25.45	$25.40
Purchase #5	$52.32	6.654%	$55.8014	$55.80	$55.80	$55.80
Purchase #6	$158.46	8.442%	$171.8372	$171.84	$171.85	$171.80
Purchase #7	$142.81	7.767%	$153.9021	$153.90	$153.90	$153.90
7 purchase totals =	$752.40		$821.6015	$821.60	$821.60	$821.50