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	$144.47	13.466%	$163.9243	$163.92	$163.90	$163.90
Purchase #2	$84.53	6.519%	$90.0405	$90.04	$90.05	$90.00
Purchase #3	$116.89	5.695%	$123.5469	$123.55	$123.55	$123.50
Purchase #4	$175.86	7.667%	$189.3432	$189.34	$189.35	$189.30
Purchase #5	$18.38	10.614%	$20.3309	$20.33	$20.35	$20.30
Purchase #6	$132.43	7.215%	$141.9848	$141.98	$142.00	$142.00
Purchase #7	$241.26	5.148%	$253.6801	$253.68	$253.70	$253.70
7 purchase totals =	$913.82		$982.8507	$982.84	$982.90	$982.70