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	$223.79	11.440%	$249.3916	$249.39	$249.40	$249.40
Purchase #2	$76.90	7.410%	$82.5983	$82.60	$82.60	$82.60
Purchase #3	$110.50	3.258%	$114.1001	$114.10	$114.10	$114.10
Purchase #4	$11.38	13.151%	$12.8766	$12.88	$12.90	$12.90
Purchase #5	$141.83	7.137%	$151.9524	$151.95	$151.95	$152.00
Purchase #6	$124.52	9.148%	$135.9111	$135.91	$135.90	$135.90
Purchase #7	$151.66	13.126%	$171.5669	$171.57	$171.55	$171.60
7 purchase totals =	$840.58		$918.3970	$918.40	$918.40	$918.50