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	$228.48	9.515%	$250.2199	$250.22	$250.20	$250.20
Purchase #2	$213.73	12.439%	$240.3159	$240.32	$240.30	$240.30
Purchase #3	$239.43	4.595%	$250.4318	$250.43	$250.45	$250.40
Purchase #4	$192.53	9.274%	$210.3852	$210.39	$210.40	$210.40
Purchase #5	$23.34	9.788%	$25.6245	$25.62	$25.60	$25.60
Purchase #6	$158.54	12.765%	$178.7776	$178.78	$178.80	$178.80
Purchase #7	$31.84	5.188%	$33.4919	$33.49	$33.50	$33.50
7 purchase totals =	$1,087.89		$1,189.2468	$1,189.25	$1,189.25	$1,189.20