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	$27.36	4.570%	$28.6104	$28.61	$28.60	$28.60
Purchase #2	$209.84	7.138%	$224.8184	$224.82	$224.80	$224.80
Purchase #3	$174.40	8.184%	$188.6729	$188.67	$188.65	$188.70
Purchase #4	$212.62	12.103%	$238.3534	$238.35	$238.35	$238.40
Purchase #5	$164.75	6.126%	$174.8426	$174.84	$174.85	$174.80
Purchase #6	$40.65	11.871%	$45.4756	$45.48	$45.50	$45.50
Purchase #7	$219.92	13.507%	$249.6246	$249.62	$249.60	$249.60
7 purchase totals =	$1,049.54		$1,150.3979	$1,150.39	$1,150.35	$1,150.40