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	$96.30	6.585%	$102.6414	$102.64	$102.65	$102.60
Purchase #2	$83.63	10.626%	$92.5165	$92.52	$92.50	$92.50
Purchase #3	$78.95	10.800%	$87.4766	$87.48	$87.50	$87.50
Purchase #4	$37.54	7.386%	$40.3127	$40.31	$40.30	$40.30
Purchase #5	$22.81	5.467%	$24.057	$24.06	$24.05	$24.10
Purchase #6	$137.83	7.440%	$148.0846	$148.08	$148.10	$148.10
Purchase #7	$34.53	3.630%	$35.7834	$35.78	$35.80	$35.80
7 purchase totals =	$491.59		$530.8722	$530.87	$530.90	$530.90