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	$16.86	5.329%	$17.7585	$17.76	$17.75	$17.80
Purchase #2	$136.57	3.631%	$141.5289	$141.53	$141.55	$141.50
Purchase #3	$130.48	5.582%	$137.7634	$137.76	$137.75	$137.80
Purchase #4	$224.39	6.281%	$238.4839	$238.48	$238.50	$238.50
Purchase #5	$150.38	12.313%	$168.8963	$168.90	$168.90	$168.90
Purchase #6	$197.39	3.501%	$204.3006	$204.30	$204.30	$204.30
Purchase #7	$155.54	10.497%	$171.867	$171.87	$171.85	$171.90
7 purchase totals =	$1,011.61		$1,080.5986	$1,080.60	$1,080.60	$1,080.70