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	$69.48	13.736%	$79.0238	$79.02	$79.00	$79.00
Purchase #2	$148.69	6.846%	$158.8693	$158.87	$158.85	$158.90
Purchase #3	$32.72	4.511%	$34.196	$34.20	$34.20	$34.20
Purchase #4	$114.45	4.470%	$119.5659	$119.57	$119.55	$119.60
Purchase #5	$55.30	8.184%	$59.8258	$59.83	$59.85	$59.80
Purchase #6	$118.65	12.629%	$133.6343	$133.63	$133.65	$133.60
Purchase #7	$108.51	3.155%	$111.9335	$111.93	$111.95	$111.90
7 purchase totals =	$647.80		$697.0486	$697.05	$697.05	$697.00