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	$19.30	12.156%	$21.6461	$21.65	$21.65	$21.60
Purchase #2	$159.93	7.229%	$171.4913	$171.49	$171.50	$171.50
Purchase #3	$92.94	7.358%	$99.7785	$99.78	$99.80	$99.80
Purchase #4	$222.50	6.641%	$237.2762	$237.28	$237.30	$237.30
Purchase #5	$155.56	5.658%	$164.3616	$164.36	$164.35	$164.40
Purchase #6	$51.92	6.641%	$55.368	$55.37	$55.35	$55.40
Purchase #7	$160.41	4.774%	$168.068	$168.07	$168.05	$168.10
7 purchase totals =	$862.56		$917.9897	$918.00	$918.00	$918.10