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	$28.35	10.687%	$31.3798	$31.38	$31.40	$31.40
Purchase #2	$8.59	5.271%	$9.0428	$9.04	$9.05	$9.00
Purchase #3	$84.70	5.582%	$89.428	$89.43	$89.45	$89.40
Purchase #4	$168.77	6.745%	$180.1535	$180.15	$180.15	$180.20
Purchase #5	$237.80	12.720%	$268.0482	$268.05	$268.05	$268.00
Purchase #6	$148.93	12.495%	$167.5388	$167.54	$167.55	$167.50
Purchase #7	$178.27	12.655%	$200.8301	$200.83	$200.85	$200.80
7 purchase totals =	$855.41		$946.4212	$946.42	$946.50	$946.30