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	$14.82	3.580%	$15.3506	$15.35	$15.35	$15.40
Purchase #2	$179.78	5.616%	$189.8764	$189.88	$189.90	$189.90
Purchase #3	$240.62	6.715%	$256.7776	$256.78	$256.80	$256.80
Purchase #4	$7.87	12.576%	$8.8597	$8.86	$8.85	$8.90
Purchase #5	$112.76	9.114%	$123.0369	$123.04	$123.05	$123.00
Purchase #6	$103.73	7.663%	$111.6788	$111.68	$111.70	$111.70
Purchase #7	$52.34	5.271%	$55.0988	$55.10	$55.10	$55.10
7 purchase totals =	$711.92		$760.6788	$760.69	$760.75	$760.80