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	$184.29	11.359%	$205.2235	$205.22	$205.20	$205.20
Purchase #2	$104.87	3.388%	$108.423	$108.42	$108.40	$108.40
Purchase #3	$24.92	10.665%	$27.5777	$27.58	$27.60	$27.60
Purchase #4	$53.97	3.561%	$55.8919	$55.89	$55.90	$55.90
Purchase #5	$195.67	13.560%	$222.2029	$222.20	$222.20	$222.20
Purchase #6	$185.79	7.322%	$199.3935	$199.39	$199.40	$199.40
Purchase #7	$137.86	3.294%	$142.4011	$142.40	$142.40	$142.40
7 purchase totals =	$887.37		$961.1136	$961.10	$961.10	$961.10