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	$111.38	7.543%	$119.7814	$119.78	$119.80	$119.80
Purchase #2	$13.66	3.350%	$14.1176	$14.12	$14.10	$14.10
Purchase #3	$131.73	8.869%	$143.4131	$143.41	$143.40	$143.40
Purchase #4	$38.42	6.609%	$40.9592	$40.96	$40.95	$41.00
Purchase #5	$225.72	5.822%	$238.8614	$238.86	$238.85	$238.90
Purchase #6	$90.80	13.267%	$102.8464	$102.85	$102.85	$102.80
Purchase #7	$249.41	11.410%	$277.8677	$277.87	$277.85	$277.90
7 purchase totals =	$861.12		$937.8468	$937.85	$937.80	$937.90