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	$37.67	12.344%	$42.32	$42.32	$42.30	$42.30
Purchase #2	$236.69	7.696%	$254.9057	$254.91	$254.90	$254.90
Purchase #3	$159.26	6.466%	$169.5578	$169.56	$169.55	$169.60
Purchase #4	$21.83	8.332%	$23.6489	$23.65	$23.65	$23.60
Purchase #5	$170.83	5.683%	$180.5383	$180.54	$180.55	$180.50
Purchase #6	$123.94	3.311%	$128.0437	$128.04	$128.05	$128.00
Purchase #7	$184.56	8.860%	$200.912	$200.91	$200.90	$200.90
7 purchase totals =	$934.78		$999.9264	$999.93	$999.90	$999.80