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	$238.45	11.807%	$266.6038	$266.60	$266.60	$266.60
Purchase #2	$225.44	10.775%	$249.7312	$249.73	$249.75	$249.70
Purchase #3	$89.31	9.175%	$97.5042	$97.50	$97.50	$97.50
Purchase #4	$33.71	10.633%	$37.2944	$37.29	$37.30	$37.30
Purchase #5	$29.91	3.699%	$31.0164	$31.02	$31.00	$31.00
Purchase #6	$215.91	4.481%	$225.5849	$225.58	$225.60	$225.60
Purchase #7	$103.96	6.350%	$110.5615	$110.56	$110.55	$110.60
7 purchase totals =	$936.69		$1,018.2964	$1,018.28	$1,018.30	$1,018.30