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	$240.32	3.370%	$248.4188	$248.42	$248.40	$248.40
Purchase #2	$115.46	13.481%	$131.0252	$131.03	$131.05	$131.00
Purchase #3	$232.28	4.834%	$243.5084	$243.51	$243.50	$243.50
Purchase #4	$11.60	12.665%	$13.0691	$13.07	$13.05	$13.10
Purchase #5	$148.28	13.755%	$168.6759	$168.68	$168.70	$168.70
Purchase #6	$38.34	9.802%	$42.0981	$42.10	$42.10	$42.10
Purchase #7	$100.93	4.121%	$105.0893	$105.09	$105.10	$105.10
7 purchase totals =	$887.21		$951.8848	$951.90	$951.90	$951.90